Sleep disorders are among the most common clinical problems encountered in medicine and psychiatry. Inadequate or nonrestorative sleep can markedly impair a patient’s quality of life.  Sleep disorders may be primary or may result from a variety of psychiatric and medical conditions.
Primary sleep disorders result from an endogenous disturbance in sleep-wake generating or timing mechanisms, often complicated by behavioral conditioning. They may be divided into the following 2 broad categories:
It is important to distinguish these primary sleep disorders from secondary sleep disorders. At times, determining whether anxiety and depression are causing sleep problems or the anxiety and depression are secondary to a primary sleep problem is difficult. (See Anxiety Disorders and Depression.)
Primary insomnia is the general term for difficulty in initiating or maintaining sleep. Because sleep requirements vary from individual to individual, insomnia is considered clinically significant when a patient perceives the loss of sleep as a problem. Insomnia may be further characterized as either acute (transient) or chronic.
Sleep is divided into the following 2 categories, each of which is associated with distinct patterns of central nervous system (CNS) activity:
REM sleep – This is characterized by muscle atony, episodic REMs, and low-amplitude fast waves on electroencephalography (EEG); dreaming occurs mainly during REM sleep
Non-REM (NREM) sleep – This is further subdivided into 4 progressive categories, termed stages 1-4 sleep; the arousal threshold rises with each stage, and stage 4 (delta), characterized by high-amplitude slow waves, is the sleep state from which arousal is most difficult
Disturbances in the pattern and periodicity of REM and NREM sleep are often found when people admit to experiencing sleep disorders.
Sleep-wake cycles are governed by a complex group of biologic processes that serve as internal clocks. The suprachiasmatic nucleus, located in the hypothalamus, is thought to be the body’s anatomic timekeeper, responsible for the release of melatonin on a 25-hour cycle. The pineal gland secretes less melatonin when exposed to bright light; therefore, the level of this chemical is lowest during the daytime hours of wakefulness.
Multiple neurotransmitters are thought to play a role in sleep. These include serotonin from the dorsal raphe nucleus, norepinephrine contained in neurons with cell bodies in the locus ceruleus, and acetylcholine from the pontine reticular formation. Dopamine, on the other hand, is associated with wakefulness.
Abnormalities in the delicate balance of all of these chemical messenger systems may disrupt various physiologic, biologic, behavioral, and EEG parameters responsible for REM (ie, active) sleep and NREM (slow-wave) sleep.
The major causes of insomnia may be divided into medical conditions, psychological conditions, and environmental problems.
Cardiac conditions that may give rise to disordered sleep include ischemia and congestive heart failure. Neurologic conditions include stroke, degenerative conditions, dementia, peripheral nerve damage, myoclonic jerks, restless leg syndrome, hypnic jerk, and central sleep apnea. Endocrine conditions affecting sleep are related to hyperthyroidism, menopause, the menstrual cycle, pregnancy, and hypogonadism in elderly men.
Pulmonary conditions include chronic obstructive pulmonary disease, asthma, central alveolar hypoventilation (the Ondine curse), and obstructive sleep apnea syndrome (associated with snoring). Gastrointestinal (GI) conditions include gastroesophageal reflux disease. Hematologic conditions include paroxysmal nocturnal hemoglobinuria, which is a rare, acquired, hemolytic anemia associated with brownish-red morning urine.
Substances that may result in insomnia include stimulants, opioids, caffeine, and alcohol, or, withdrawal from any of these also may cause insomnia. Medications implicated in insomnia include decongestants, corticosteroids, and bronchodilators.
Other conditions that may affect sleep include fever, pain, and infection.
It should be borne in mind in mind that the major psychiatric conditions now are known to have a biologic basis and thus constitute a subset of medical conditions.
Depression may cause alterations in REM sleep. As many as 40% of people with depression have insomnia. Posttraumatic stress disorder (PTSD) can produce vivid and terrifying nightmares. Anxiety disorders predispose to insomnia. The most common of these are generalized anxiety disorder, panic disorder, and anxiety disorders not otherwise specified. Thought disorders and misperception of sleep state are other potential states that cause insomnia.
Psychotropic medications, such as antidepressants, may interfere with normal REM sleep patterns. Rebound insomnia from benzodiazepines or other hypnotic agents is common.
Stressful or life-threatening events (eg, bereavement or PTSD) may cause insomnia. Shift work may disturb the sleep cycle, as may jet lag or changes in altitude. Sleep deprivation may occur as a result of an overly warm sleeping environment, environmental noise, or frequent intrusions (such as occur in an intensive care unit [ICU]).
Approximately one third of all Americans have sleep disorders at some point in their lives. Between 20% and 40% of adults report difficulty sleeping at some point each year, and about 17% of adults consider the problem to be serious. Sleep disorders are a common reason for patient visits throughout medicine. Approximately one third of adults have insufficient sleep syndrome. Twenty percent of adults report chronic insomnia.
Age- and sex-related demographics
Increasing age predisposes to sleep disorders (5% incidence in persons aged 30-50 years and 30% in those aged 50 years or older). People who are elderly experience a decrease in total sleep time, with more frequent awakenings during the night. Elderly persons also have a higher incidence of general medical conditions and are more likely to be taking medications that cause sleep disruption.
People who are elderly may have widespread or multisite pain that is associated with sleep difficulty, according to the Maintenance of Balance, Independent Living, Intellect, and Zest in the Elderly study (MOBILIZE) study. 
Primary insomnia is more common in women, with a female-to-male ratio of 3:2. Hormonal variations during the menstrual cycle or during menopause may cause disruptions in sleep. Obstructive sleep apnea (OSA) is more common in men (4%) than in women (2.5%).
The prognosis varies widely, depending on the cause of the insomnia or other sleep disorder. For example, insomnia due to OSA resolves with successful treatment of the apnea, whereas insomnia due to refractory major depression is itself refractory until a successful treatment can be found for the depression.
Chronic insomnia is associated with an increased risk of depression and accompanying danger of suicide, anxiety, excess disability, reduced quality of life, and increased use of health care resources.
Insufficient sleep can result in industrial and motor vehicle crashes, somatic symptoms, cognitive dysfunction, depression, and decrements in daytime work performance owing to fatigue or sleepiness.
Yaffe et al suggest that older women with sleep-disordered breathing (characterized by recurrent arousals from sleep and intermittent hypoxemia) have an increased risk of developing cognitive impairment compared with those without sleep-disordered breathing. 
One study suggests that among police officers in the United States and Canada, sleep disorders are common and are significantly associated with an increased risk of self-reported adverse outcomes in terms of health, performance, and safety. 
All individuals should be taught and encouraged to practice good sleep hygiene (see Treatment). Educating patients’ families about proper sleep hygiene is imperative, especially because bed partners can be adversely affected by sleep disorders such as OSA. Patients should be instructed to use the bed for sleep and sex only (no television watching or reading in bed). They should also be warned to not drive or operate machinery while taking sedative-hypnotic medications. Document these admonitions clearly in the medical record.
For patient education resources, see the Mental Health and Behavior Center and the Sleep Disorders Center, as well as Disorders That Disrupt Sleep (Parasomnias), Insomnia, Primary Insomnia, REM Sleep Behavior Disorder, Understanding Insomnia Medications, Sleep Disorders in Women, Sleep Disorders and Aging, and Sleeplessness and Circadian Rhythm Disorder.
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