Introduction to Sleep Disorders
by Chris Craig, MSN, ARNP

What is Sleep?
     Overview of normal sleep
Sleep Disorders
What can a Practitioner Do?
     Taking a history
     Referral to Sleep Specialists and Sleep Centers

One of the most important processes of life is also one of the most overlooked in family practice, namely sleep. Humans spend roughly one third of their lives in this state and sleep, or the lack of it, and its quality impacts nearly every system in the body and also has a major impact on humans' quality of life. For this reason, it is important that we in the health care field assess the status of patient's sleep as we would a patient's pulmonary, cardiac or mental health status. Thus, the purpose of this article, and others to follow, is to help a practitioner understand various aspects of normal sleep and its disorders and to aid the diagnosis and treatment of sleep disorders.

What is Sleep?

The purpose of sleep is still not completely understood. In the past, sleep was thought to that state between life and death. The state of sleep has been the stuff of poets, writers, philosophers and even physicians for countless centuries. "There is only one thing . . . that I dislike in sleep; 'tis that it resembles death; there's very little difference between a man in his first sleep, and a man in his last sleep". (Miguel de Cervantes (15471616), Spanish writer. Sancho Panza, in Don Quixote, pt. 2, bk. 6, ch. 35 (1615; tr. by P. Motteux).)

"We term sleep a death . . . by which we may be literally said to die daily; in fine, so like death, I dare not trust it without my prayers. (Sir Thomas Browne (160582), English physician, author. Religio Medici, pt. 2, sct. 12 (1643))

Each day is a little life: every waking and rising a little birth, every fresh morning a little youth, every going to rest and sleep a little death. (Arthur Schopenhauer (17881860), German philosopher. Parerga and Paralipomena, "Counsels and Maxims" (1851)).

This concept of sleep has been present for centuries and is still with us, to some extent, even today. How often is the euphemism of sleep used to describe one who has died.

This view of sleep as a state between life and death was not limited to the ancient physicians, or writers or philosophers. Robert MacNish wrote in The Philosophy of Sleep in the early 1800's that sleep was the intermediate state between wakefulness and death. Until recent years, sleep was thought to be an inactive state. Falling asleep was thought to be a reduction of sensory input, which resulted in the reduction of brain activity leading to sleep. Waking up and wakefulness was therefore thought to be the reversal of this process. Little or no distinction was seen between sleep and other states such as coma, hypnosis, anesthesia and even hibernation. Dreams were thought to be fleeting interruptions of this reduced activity. In the last century, research by Nathaniel Klietman, William Dement, and many others lead to changes in these ideas of sleep.

There is now thought to be three distinct states of human existence: wakefulness, non-rapid eye movement sleep (NREM) and rapid eye movement sleep (REM). A full discussion of wakefulness is beyond the scope of this article; however, the impact of sleep disorders on wakefulness will be touched on in this article as well as others.

Overview of Normal Sleep

In the following discussion, please keep in mind that many, many factors affect sleep. Though a "normal sleep" pattern can be discussed, this is a generalization. The sleep of newborns is very different that that of adults. As one ages through childhood, sleep can change dramatically. Thus the normal sleep of adolescents and their sleep needs is different than the sleep of children and the sleep of adults. Even for adults, there can be changes in sleep across the aging process. However, for this article, the normal sleep is generalized for the normal young adult. In future articles, the differences across the ages will be discussed.

Sleep Cycles

In the past, sleep was thought to normally progress throughout the night with dreaming occurring right before awakening. Today, in 'common wisdom', this view of sleep is still held. However, this is not an accurate view of sleep. In brief, we enter sleep thorough NREM sleep, with REM sleep occurring approximately 90 minutes later. Thus, throughout the night we cycle through the various stages of sleep with a period of about 90 minutes. It is not unusual to measure brief periods of wakefulness at the end of a sleep cycle, though more often than not, the person is unaware of this short period of wake.

NREM and REM sleep continue to alternate throughout the night in a cyclical fashion. However, the properties of the various stages of sleep change and the night, and sleep, progresses. The REM sleep stages become longer across the night. It is not unusual to see little if any REM sleep during the first sleep cycle and observe extended periods of REM sleep in the later cycles, sometimes lasting 30 minutes or longer. Stages 3/4 NREM sleep occur less often as the night progresses and may disappear completely from the later cycles. The amount of stage 2 NREM sleep per cycle increases through the night.

Length of Sleep

The length of normal sleep is quite variable and dependent on many factors, with genetics thought to play a major role. The day to day factors that affect our length of sleep, e.g. life stressors, staying up late, the alarm clock, etc., are superimposed on a framework of personal sleep need. Thus, it is difficult to state what one person's sleep need should be, what his or her optimum length of sleep should be without detailed investigation. That being said, in general, a normal length of sleep should be approximately 8.5 to 9 hours. Given in our society that people obtain 6-8 hours of sleep on average, how sleep deprived are we and what effect does this have on society?

Sleep Stages

NREM Sleep NREM sleep constitutes 75% to 80% of sleep in a normal adult and has been divided into four stages. The division of these stages can sometimes be arbitrary.

Stage 1 sleep is a transition between wakefulness and sleep. This stage may persist for only a few minutes at the onset of sleep. This stage can also occur as a transition stage throughout the night. The electroencephalogram (EEG) shows slowing of the brain waves and the relatively low-voltage, mixed frequency activity. Slow eye movements commonly precede the EEG transition to Stage 1 sleep. Muscle tone is maintained during all NREM sleep though the level of this tone may diminish. However, the person may not perceive sleep onset during this time. Stage 2 NREM sleep is distinguished from Stage 1 NREM sleep by the presence of sleep spindles and K complexes. These occur episodically throughout stage 2 NREM sleep. As sleep progresses there is a gradual appearance of high voltage slow wave activity and these will appear often enough to meet the criteria for Stages 3and 4 sleep. Stages 3 and 4 require significant stimulus to awaken the person. The stages of sleep are often refereed to as slow wave sleep, or deep sleep. Stages 3 and 4 sleep represent the least percentage of sleep through the night. Often, in testing situations, because of being tested, a diminished amount of Stage 3 or 4 sleep may be noted. This has lead to some myths about certain disorders or syndromes that are 'caused' by a lack of "deep sleep".

REM Sleep REM sleep is usually 20% to 25% of sleep and occurs in four to six specific episodes throughout the night.

In REM sleep there is an increase in brain activity as noted on the EEG. Bursts of Rapid eye movements are noted (hence the name Rapid Eye Movement Sleep). Muscle tone is significantly diminished and a state of atonia exists. Though the body may look extremely relaxed due to atonia, brain activity is high. Typically, during this stage of sleep, dreaming occurs.

Sleep Disorders


Disorders of sleep can affect 10% to 20% of the population. Sleep disorders can be life disrupting, affecting a person socially and psychologically. They can also be life threatening, for example, excessive daytime sleepiness leads to increased motor vehicle accidents and workplace accidents. Sleep disorders, despite the toll on the person, the family and society are largely unrecognized. Health care providers must learn to inquire about the possibility of sleep disorders and learn to distinguish the more serious sleep problems from the less serious sleep disturbances such as transient insomnia related to situational anxiety.

Three broad classifications of sleep disorders are used in the International Classification of Sleep Disorders (ICSD). These categories are the dyssomnias, the parasomnias, and medical- psychiatric sleep disorders. The dyssomnias are disorders that produce either insomnia or excessive sleepiness. These are the major disorders associated with disturbed sleep. These disorders include primary insomnia, obstructive sleep apnea, narcolepsy, restless legs syndrome, and various circadian rhythm disorders. Parasomnias consist of the disorders that are undesirable physical phenomena that occur during sleep. Generally they are disorders of arousal, partial arousal, and sleep stage transitions. These disorders include sleepwalking, sleep terrors (night terrors), REM behavior disorder, and rhythmic movement disorders. The ICSD is a revision of the original classification system, which was necessary due to problems with the Diagnostic Classification of Sleep and Arousal Disorders (DCSAD).

The DCSAD was based on symptoms (Difficulty Initiating and Maintaining Sleep (DIMS), Disorders of Excessive Somnolence (DOES), etc.) and often there was an overlap in the classification system that could lead t confusion. New disorders were identified and there was additional information on many of the original disorders. However, the DCSAD system is useful as a framework for discussion of sleep disorders and so a modified version of the DCSAD system will be used here for the presentation of some of the major sleep disorders. It is important when obtaining a history of the sleep complaints to keep both classifications in mind, and remember that often there can be overlap in the symptoms.


Many disorders can cause difficulty for a patient in falling asleep when they wish or staying asleep once they have fallen asleep. These disorders can range from a transient insomnia, chronic insomnia, sleep-wake schedule problems, or even parasomnias. These disorders, especially the insomnias, can be one of the most frequently seen complaints on a general practice.


The complaints can be difficulty in falling asleep in the beginning of the night, problems falling back to sleep after awakening in the middle of the night, or early morning awakening, much earlier than the person would like. The perceived insufficient sleep will lead to complaints of non-restorative sleep, fatigue or sleepiness during the day, difficulty concentrating on normal daily tasks, or may be thought to be the cause of more serious medical problems.

In a recent Gallup Poll, 36% of the respondents reported insomnia, with 9% considering their insomnia serious. More women than men complain about insomnia. The incidence of insomnia appears to increase with age. This may be in part due to poor sleep habits, the presence of other medical or psychological disorders, and intrinsic sleep disorders in the elderly. The insomnia can be transient, short-term or recurrent insomnia, or chronic or long-term insomnia.


Transient insomnia, insomnia lasting a few days, may develop in normal sleepers. Typically, this type of insomnia occurs as a result of acute stress, for example, stress at work, an upcoming presentation or test. Short term psychological stressors, for example family or financial stressors may also trigger transient insomnia. Occasionally, transient insomnia may be prolonged due to the prolonged nature of the stressors and lead to a chronic insomnia. Transient insomnia can recur and which is known as intermittent or recurrent insomnia.


Insomnia can be a continuous problem lasting months or years. This is known a chronic insomnia or long-term insomnia. The causes of chronic insomnia can include psychiatric factors, for example, depression or anxiety. Medications can also lead to chronic insomnia. The two most commonly used drugs that can cause insomnia are alcohol and caffeine. Medical illnesses especially chronic illnesses, can also contribute to long term insomnia, for example, CHF or PND or even asthma. Sleep hygiene issues may also contribute to on-going complaints of insomnia.

Sleep-Wake Schedule Disorders

People have an internal clock that helps govern their bodily functions. This circadian rhythm helps determine the sleep-wake cycle for an individual. In some people, there is difficulty in adjusting the internal circadian rhythm of the sleep cycle to the rest of the world. In others, there is a struggle to adjust to a new situation. The first group of disorders includes delayed sleep phase syndrome, and advanced sleep phase syndrome. The second group include shift workers who need to adjust to change work schedules (shift work sleep disorders) and travelers across multiple time zones (jet lag).

Delayed Sleep Phase Syndrome (DSPS) In patients with this disorder, the time to sleep has been delayed to a later time then is considered optimal. The patient, in extreme cases, may be awake until dawn trying to fall asleep. Once asleep, the patient will have normal sleep times and feel well rested upon awakening following normal sleep. Frequently, they become more awake as the day progresses and can be awake and alert late into the night. Frequently, adolescents drift into a delayed sleep phase syndrome, going to bed later and later, having a hard time awakening for school or work, and sleeping late into the morning or afternoon when they can.

Advanced Sleep Phase Syndrome (ASPS) This is a less common disorder than DSPS. The patient will complain of the inability to stay awake after 20:00 or earlier yet awaken fully refreshed at 3:00. The practitioner needs to be aware of any underlying psychological disorders where an early bedtime would help avoid social interactions. Medications may also lead to increased drowsiness in the evening and, over time, entrain a pattern of early bed times. Age may also play a factor.

Shift work Sleep Disorder The shift workers most common complaint is disrupted sleep due to difficulty initiating and maintaining sleep with resulting poor sleep quality. They will experience chronic drowsiness and may doze off at work with resulting accidents. The resulting sleep loss and the patient's means to overcome the problem, alcohol, sedatives, stimulates, etc.) contribute to the problem. A good sleep history to eliminate underlying psychological and medical factors is important.


RLS/PLMS Restless leg syndrome is a disorder characterized by an unpleasant, hard to define, creeping sensation primarily in the lower legs. Descriptions such as 'cola in the veins', 'the hebbie-jebbies', and 'jittery legs' are not uncommon. The sensation is normally felt between the knee and the ankle, is bilateral but may be asymmetric. Rarely does it occur unilaterally. The sensations may also affect the thighs and the arms. The symptoms occur at rest just prior to falling asleep but may also occur when sitting for long periods, for example, on a long car or plane trip, in the theater or at the movies. Partial or complete relief will occur with movement but the sensation will reoccur when the movement stops. Because of the severity, significant disruption in the ability to fall asleep occurs.

Periodic limb movements in sleep are periodic episodes of rhythmic and stereotypic limb movements while the patient is asleep. These movements occur primarily in the legs and there is an extension of the toes with a flexion of the ankle, knees and hip. These movements may last 0.5 to 5 seconds and may recur every 15 to 40 seconds. The movements may be accompanied by arousals or awakenings, though the patient is usually unaware of the movements. Usually complaints of excessive daytime sleepiness are present due to the arousals throughout the night. Other complaints come from bed partners who complain of their sleep being disrupted by the movement. Frequently, a good history will identify PLMS in patients with complaints of RLS. However, PLMS can found without RLS.

PLMS is rarely found in children but occurs more often with aging. RLS is typically diagnosed in middle age but on careful history the restlessness was noted in youth. It is unclear what percentage of the population experiences RLS or PLMS, but it is thought to be between 1% and 5%.

Sleep Walking and Night Terrors

Sleepwalking (somnambulism) and night terrors are parasomnias of arousal that occur predominately, but not exclusively, in children. They are noted for their motor or autonomic activity occurring during a partial arousal from sleep thought to be from slow wave sleep.

In children, often they don't leave the bed but make repetitive movements while sitting up in bed. When they do "walk around" the house, they have their eyes open, avoiding bumping into familiar objects. Behaviors tend to be simple and there tends to be little vocalization. However, there can be more involved behavior, and at times, inappropriate. They may act as if they want to escape, may open doors to the outside, scream, or other actions like urinating in inappropriate places. If awakened, they will be disoriented for several minutes. Later recall of the events is hazy at best and often is completely lacking. They may report 'dreams' but on further questioning these dreams are very vague or fearful images as opposed to REM dreams.

Night terrors are a more severe and frightening partial arousal from sleep, especially for family or household members. Similar to sleepwalking, they occur during the first few hours of sleep when slow save sleep predominates. These episodes though often begin with a loud scream or cry, with the person showing fear or anxiety. They are often impossible to consul and, as quickly as the episode began, it will end, often within a few minutes. The classic scenario is one of a 4-6 year old child screaming with fear for mom or dad. The parent then tries to comfort the child who will shove the parent away while still screaming for their mom or dad. Suddenly the child calms down, lies back down, and is fast asleep. The next morning there is no recollection of the event.

A careful history needs to be obtained, especially if there is any history of any harmful behavior. These episodes may mimic other REM behavior disorders, nightmares, seizure disorders, panic attacks, or dissociative states. However, most children will grow out of the symptoms though various treatments may be necessary.


With this broad group of disorders, the usual complaint is not one of an inability to fall asleep and stay asleep but an inability not to fall asleep or not to awaken easily in the morning. The patient will complain of excessive daytime sleepiness (EDS) or hypersomnulence. They will find themselves nodding in class, at their desk, or even behind the wheel. There may be complaints of driving for miles and not realizing that they drove that way. They may get off at the wrong exit, miss their stops on busses and trains. They may even be involved in accidents, sometimes fatal. Many sleep disorders can have as their primary complaint EDS, but some of the more common sleep disorders include obstructive sleep apnea, narcolepsy, and idiopathic hypersomnia.

Obstructive Sleep Apnea (OSA)

Sleep Apnea is the second most common sleep disorder affecting between 10% and 20% of the adult population, insomnia being the most common. This problem can also be found in children. Patients with sleep apnea have trouble breathing or even stop breathing during sleep. The severity of OSA can range from mild (10 times per hour) to serious (more than 30 times per hour). These pauses in breathing must last at least 10 seconds and be accompanied by a significant drop on oxygen saturation to be counted as an apnic event. Patients though can stop breathing for 2 minutes or have a reduction in oxygen saturation to less than 50% because of the apnea. Most are not aware of having any problem.

Normally when a person breathes, there is a large negative pressure within the chest. This negative pressure eventually leads to air rushing in to fill the lungs. In order for the air to move freely, the airway from the pharynx to the lungs must remain patent. However, in OSA, the soft tissue collapses, restricting or even blocking the normal flow of air. The respiratory drive is still present, the patient tries and struggles to breath, but no air enters the lungs. Eventually, due to the reduction in oxygen saturation or even the struggle to breathe, the patient experiences a brief arousal. This interrupts sleep, increases general muscle tone, opens the upper airway, and with a loud snore or snort, breathing again resumes. As mentioned above, this process can occur more than 30 times an hour throughout the night.

Loud snoring, daytime sleepiness and tiredness are the most common signs. Patients most often complain of excessive sleepiness or hypersomnulence, but others in the household may have as their primary complaint the loud snoring. Sometimes this snoring can be loud enough to be heard outside the house. The patient's sleep is restless, and morning headaches are not uncommon. The patient may fall asleep on the job or behind the wheel and poor school performance is not uncommon in children.

Sleep apnea is associated with hypertension, heart disease, and stroke. Approximately 50% of adults with OSA have hypertension. The patient is also at risk from injury due to the related hypersomnulence. There is an increased risk of accidents on the job, at home and behind the wheel.

Though a patient may complain of excessive daytime sleepiness (EDS), many other sleep disorders may be the cause. Even with a history of snoring, apnea may not be present. Snoring is a symptom of relaxed muscle tone in the upper airway, so patients who snore may not necessarily have OSA. Restless sleep may be caused by OSA or by PLMS, medication disrupting sleep or other causes. Thus, a good history is important


Narcolepsy is another disorder of excessive sleepiness or hypersomnulence. The etiology of narcolepsy is unclear but genetic factors are important. Narcolepsy is not rare, occurring in possibly 0.05% to 0.1% of the population. This disorder is characterized by excessive sleepiness that is typically associated with cataplexy and other REM phenomena such as sleep paralysis and hypnagogic hallucinations.

The sleepiness of narcolepsy is irresistible. The patient often may struggle to remain awake and alert with much effort but eventually it proves impossible to remain awake. Cataplexy is considered a primary feature in narcolepsy. A sudden loss of muscle tone will occur, typically affecting the legs but may also affect the arms, neck, or jaw and a head drop, slurred speech, or facial sag may be the only sign. Cataplexy follows an emotional stimulation. Sleep paralysis is a sudden, short lived, generalized inability to move or speak while falling asleep. The muscle control can return within minutes but even a light touch by someone can cause the muscle tone to return. These episodes are often accompanied by hallucinations. These may be visual, seeing someone or something in the room, tactile or auditory.

Recurrent daytime sleepiness and cataplexy are the primary features of narcolepsy. Thus a good history is important both to not overlook the possibility of narcolepsy, but also so as not to label someone present with EDS due to other sleep disorders as having narcolepsy. The possible occurrence of other REM phenomena must also be explored.

Idiopathic hypersomnia

Idiopathic hypersomnia is a syndrome of persistent EDS. Its etiology is unclear. Patients with this disorder have complaints of a nearly irresistible need to sleep during the day. These naps can be 60 minutes or longer and are unrefreshing. When not sleeping, the patient may have trouble concentrating due to the drowsiness they experience. The EDS will occur despite normal sleep times or even prolonged sleep. Though in extreme cases, the patient may be said to have narcolepsy, they do not have cataplexy, sleep paralysis or hallucinations associated with narcolepsy.

What a Practitioner Can Do

Taking a history

An accurate history is of significant importance in the evaluation of sleep disorders. However, one of the first steps in the evaluation of sleep disorders is the identification of a potential disorder. This is frequently overlooked. Given that over 30% of the population may have some degree of a problem with sleep, it is paramount that this area be addressed in clinical visits.

By beginning simply, the possibility of an underlying problem can begin to surface. A good first question would be "How are you sleeping?". If there appears to be a problem it would be helpful to identify the duration of the symptoms and their pattern. Keep in mind any other medical or psychological factors that may impact the patient's sleep. It's important to also include other family or household members in the discussion as the person with a sleep disorder may not fully recognize that a problem exists. Also, the cause of the sleep problem may involve another family member.

It is important to ask how daytime functioning has been affected. At this point, the usual symptom approach should be used, i.e. what makes the symptoms better, worse, what has been tried in the past, how successful have they been, etc. In some cases, a sleep diary or sleep log can prove useful. The sleep log can help identify patterns, show evidence of sleep schedule disruptions, or help clarify the severity of the sleep disorder. Frequently, focusing on the sleep disorder complaint for a few minutes is all that's needed to identify a problem exists, give some indication of the severity, and, occasionally, what the underlying etiology may be. Further follow-up in the office or a referral to a sleep specialist can then be arranged.

Referral to Sleep Specialists and Sleep Centers

Who Are These People?

A sleep specialist should evaluate any patient with a suspected sleep disorder. Sleep specialists provide for a through evaluation and are often available for consultation of sleep related complaints. This is a relatively new field of expertise, and the number of clinicians in this specialty area is small but growing.

The American Academy of Sleep Medicine (AASM) has established the standards for the evaluation and treatment of sleep disorders. Doctors can become board certified after further study in sleep physiology through fellowship programs, graduate courses, or through practice at a sleep disorder center under the direction of a board certified sleep. At this time, there is no special certification program for nurse practitioners. Frequently, the sleep specialist is connected to a sleep center. An accredited sleep center is one that has met the standards established by the AASM. These centers are located in nearly every state.

The initial evaluation by a sleep specialist may last over an hour. Depending on the suspected sleep disorder, further testing in the sleep laboratory may be indicated. Follow-up visits to review test results, explain treatment options or evaluate treatment results may be indicated.

Testing and Follow-up

Sleep testing allows for the evaluation of sleep and its disorders. However, it is not indicated for all sleep disorders. Sleep testing is performed by means of polysomnography (PSG) and the multiple sleep latency test (MSLT). The patient sleeps in a private room through the usual sleep time, normally overnight. The room has a comfortable bed (not a hospital bed) and is isolated, as much as is possible, from external light and sound.

Prior to the actual testing, electrodes and other sensors are attached to the body. On the head, electrodes are used to monitor brain activity by a limited EEG. This helps to distinguish the sleep stages and wakefulness. Electrodes are attached to the outside corner of each eye to record eye movements (EOG). On the chin, the electrodes detect jaw muscle tone (EMG). Electrodes on the chest record heart rhythm to detect arrhythmias. Electrodes are also placed on the legs to detect any abnormal movements during sleep (EMG). Sensors are placed around the chest and abdomen to record respiratory effort during sleep. A device is place below the nose to detect airflow through the mouth and nose. Finally, an oximeter is clipped to a finger or earlobe to record oxygen saturation. Minimal discomfort occurs to the patient. The data collected allows evaluation of the patient's sleep and helps identify any pathology. The MSLT is also used to identify certain sleep disorders. This test attempts to quantify daytime sleepiness. The patient is instructed to lie down in their bed and try to fall asleep. These naps are performed four to five times during the day approximately every two hours. Normal sleepers may require 10-20 minutes to fall asleep. Pathologically sleepy patients may fall asleep in less than five minutes.

These are the basic studies used for the evaluation of sleep disorders. No adequate alternative method has been developed, though in certain situations the PSG testing may be performed in the patient's home.

Last updated:  November 22, 2000


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