The International Classification of Sleep Disorders (ICSD-2)  defines insomnia as a difficulty in initiating/maintaining sleep or non-restorative sleep accompanied by decreased daytime functioning persisting for a period of at least 4 weeks. Insomnia afflicts about 10% of the population in western industrialized countries. Primary Insomnia (PI) occurs in about 2 to 4% of the adult population . More frequently, however, insomnia occurs as a co-morbid condition together with other disorders.
Citation: Baglioni C, Riemann D (2012) Cognitive-Behavioral Treatment for Insomnia Comorbid with Psychiatric Disorders. J Sleep Disorders Ther 1:e112. doi: 10.4172/2167-0277.1000e112