Insomnia is defined by a repeated difficulty with sleep initiation, duration, consolidation, or quality that occurs despite adequate time and opportunity for sleep and results in some form of daytime impairment. Among adults, reported difficulties initiating or maintaining sleep are typical. Concerns about nocturnal wakefulness or insufficient amounts of sleep usually accompany these complaints.
Insomnia is a symptom that often arises from primary medical illnesses, mental disorders, and other sleep disorders. It may also arise from use, abuse, or exposure to certain substances such as caffeine.