sleep disorder
a persistent disturbance of typical sleep patterns (including the amount, quality, and timing of sleep) or the chronic occurrence of abnormal events or behavior during sleep. In DSM–IV–TR, sleep disorders are broadly classified according to apparent cause, which may be endogenous or conditioning factors (primary sleep disorders), another mental disorder, a medical condition, or substance use. Primary sleep disorders are subdivided into dyssomnias and parasomnias. DSM–5, which encompasses sleep disturbances under the rubric sleep–wake disorders, eliminates sleep disorders related to another mental disorder and to a general medical condition as distinct entities in order to avoid making causal assumptions about comorbid disorders. A classification system introduced in 1979 by the Association of Sleep Disorders Centers groups sleep disorders according to individuals’ presenting symptoms:
disorders of initiating and maintaining sleep; disorders of excessive somnolence; disorders of the sleep–wake cycle schedule; and dysfunctions associated with sleep, sleep stages, or partial arousals.