Insomnia is most frequently defined by an individual's report of sleeping difficulties. While the term is sometimes used in sleep literature to describe a disorder demonstrated by polysomnographic evidence of disturbed sleep, survey studies define insomnia simply as a positive response to either of two questions: ""Do you experience difficulty sleeping?"" or ""Do you have difficulty falling or staying asleep?"" Thus, insomnia is most often thought of as both a sign and a symptom that can accompany several sleep, medical and psychiatric disorders, characterized by persistent difficulty falling asleep and/or staying asleep or sleep of poor quality. Insomnia is typically followed by functional impairment while awake.
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