The term insomnia is used in a variety of ways in the medical literature and popular press. Most often, insomnia is defined by the presence of an individual's report of difficulty with sleep. For example, in survey studies, insomnia is defined by a positive response to either question, “Do you experience difficulty sleeping?” or “Do you have difficulty falling or staying asleep?” In the sleep literature, insomnia is sometimes used as a term to describe the presence of polysomnographic evidence of disturbed sleep. Thus, the presence of a long sleep latency, frequent nocturnal awakenings, or prolonged periods of wakefulness during the sleep period or even frequent transient arousals are taken as evidence of insomnia.1 Thus, insomnia has been thought of both as a symptom and as a sign. However, for the purpose of this paper, the term insomnia will be used as a disorder with the following diagnostic criteria: (1) difficulty falling asleep, staying asleep or nonrestorative sleep; (2) this difficulty is present despite adequate opportunity and circumstance to sleep; (3) this impairment in sleep is associated with daytime impairment or distress; and (4) this sleep difficulty occurs at least 3 times per week and has been a problem for at least 1 month.

What qualifies insomnia to be considered a disorder? A disorder is a condition associated with negative consequences, and importantly, these consequences are not a normal result of the condition but rather the result of some sort of pathological response. In the present discussion, the consequences of insomnia can not merely be the normal consequence of sleep loss.