Insomnia is most often defined by sleeping difficulties. While the term is sometimes used in sleep literature to describe a disorder demonstrated by polysomnographic evidence of disturbed sleep. insomnia makes difficulties in initiating and/or maintaining sleep, or nonrestorative sleep, associated with impairments of daytime functioning or marked distress for more than 1 month. Primary insomnia is a sleep disorder not attributable to a medical, psychiatric, or environmental cause.