Insomnia is defined as a persistent difficulty with sleep initiation, duration, consolidation, or quality that occurs despite adequate opportunity and circumstances for sleep, and results in some form of daytime impairment.

Chronic insomnia is characterized by symptoms that occur at least three times per week for at least three months. Insomnia that lasts or less than three months is known as short-term insomnia.

Chronic insomnia disorder occurs in about 10% of the population, but the prevalence of transient insomnia symptoms is much higher (30% to 35% of the population). It is more common in women and its incidence increases with age.