Disturbances of sleep are probably more common than we realize.
Abnormalities of sleep and wakefulness are understood in relationship to agreed-on “normal” patterns of sleep and wakefulness. A wide range of normal sleep and wakefulness experiences occur at different ages and in different cultures, and the vagueness of terminology used to describe subjective qualities of different states of consciousness makes it difficult to define and quantify symptoms of abnormal sleep and wakefulness. Different sleep 'disorders' have been described including:
Disturbances of sleep or wakefulness caused by disruptions in the body’s normal circadian rhythms are commonplace in developed countries because of steadily increasing jet travel and the widespread practice of shift work. Circadian rhythm disturbances often result in clinically significant insomnia and excessive daytime sleepiness.
Narcolepsy is a severe disorder of wakefulness characterized by sudden onset sleep attacks, sleep-onset hallucinations, sleep paralysis, and cataplexy—the sudden loss of muscle tone precipitated by intense emotions. In contrast to dyssomnias, parasomnias are defined in relation to abnormal events that take place during sleep, including nightmares, sleep terrors, and sleepwalking. Rapid eye movement (REM) sleep behavior disorder is a rare parasomnia in which nightmares during REM sleep are accompanied by purposeful movements (i.e., the normal paralysis of voluntary muscles during sleep is lost), sometimes resulting in harm to the patient or his or her partner. The American Academy of Sleep Medicine defines excessive sleepiness as “a complaint of difficulty in maintaining desired wakefulness or a complaint of an excessive amount of sleep” (American Sleep Disorders Association, 1997). Defining abnormal patterns of sleep and wakefulness in different ways has practical clinical consequences because disparate diagnostic criteria lead to different clinical assessment and treatment approaches, which translate into significant differences in outcomes (De Valck & Cluydts, 2003).
Complaints of excessive daytime sleepiness and disturbed sleep are probably under-reported. Whereas some individuals view persisting problems falling asleep or intermittent nighttime awakenings as normal, others interpret the same pattern as abnormal or impairing and seek medical attention. Subjective differences also separate individuals who experience daytime somnolence. Epidemiologic studies show that many people who cope with severe insomnia or daytime somnolence for many years often interpret these symptoms as “tiredness,” and subsequently under-report them as debilitating symptoms (Dement, Hall, & Walsh, 2003).
Many individuals who report disrupted sleep also report daytime somnolence or fatigue, but not all individuals who complain of chronic fatigue have problems sleeping or difficulties staying awake in the daytime. Many individuals who have difficulty falling asleep or staying asleep have a medical problem, substance abuse, or a psychiatric disorder that was diagnosed after their sleep disturbance. Patients with complicated medical or psychiatric histories frequently report changing symptoms of insomnia or daytime sleepiness, and it is often impossible to establish a discrete cause of their symptoms. To add to these complications, what is considered “normal” sleep continues to change throughout the life span, and healthy elderly individuals commonly report reduced nighttime sleep, fragmented sleep, and increased daytime napping. Thus normal sleep and wakefulness among the elderly is probably quite different than normal sleep in young or middle-aged people.