Most adults have difficulty sleeping at some time in their lives, with problems falling asleep, staying asleep, or having nonrestorative sleep. When these symptoms continue for ≥1 month and are associated with daytime dysfunction or distress, they reach the status of an insomnia disorder. Roughly 10% of adults in the United States have an insomnia disorder (hereafter referred to as insomnia), ie, that which is present on most nights and lasts ≥4 weeks. Insomnia can be primary, in which the sleep disturbance exists in the absence of co-existing medical or psychiatric disorders, or comorbid, when it is accompanied by one of these disorders.

Although a diagnosis of insomnia requires difficulty with sleep, insomnia is a 24-hour disorder. Individuals with insomnia describe difficulties with concentration, fatigue, and mood, which both influence, and are influenced by, the sleep disturbance. In addition, insomnia is associated with a substantially elevated risk of incident major depressive disorder (MDD), panic disorder, and substance abuse disorders. There is also emerging evidence that insomnia increases the risk for incident hypertension and diabetes.