Population-based estimates indicate that about one-third of adults report insomnia symp- toms, 10%—15% experience associated daytime impairments, and 6%—10% have symptoms that meet criteria for insomnia disorder. Insomnia disorder is the most prevalent of all sleep disorders. In primary care settings, approximately 10%—20% of individuals complain of significant insomnia symptoms. Insomnia is a more prevalent complaint among fe- males than among males, with a gender ratio of about 1.44:1. Although insomnia can be a symptom or an independent disorder, it is most frequently observed as a comorbid con- dition with another medical condition or mental disorder. For instance, 40%—50% of indi- viduals with insomnia also present with a comorbid mental disorder.
The onset of insomnia symptoms can occur at any time during life, but the first episode is more common in young adulthood. Less frequently, insomnia begins in childhood or ad- olescence. In women, new-onset insomnia may occur during menopause and persist even after other symptoms (e.g., hot ﬂashes) have resolved. Insomnia may have a late-life onset, which is often associated with the onset of other health-related conditions.
Insomnia can be situational, persistent, or recurrent. Situational or acute insomnia usu- ally lasts a few days or a few weeks and is often associated with life events or rapid changes in sleep schedules or environment. It usually resolves once the initial precipitating event subsides. For some individuals, perhaps those more vulnerable to sleep disturbances, in- somnia may persist long after the initial triggering event, possibly because of conditioning factors and heightened arousal. The factors that precipitate insomnia may differ from those that perpetuate it. For example, an individual who is bedridden with a painful injury and has difficulty sleeping may then develop negative associations for sleep. Conditioned arousal may then persist and lead to persistent insomnia. A similar course may develop in the context of an acute psychological stress or a mental disorder. For instance, insomnia that occurs during an episode of major depressive disorder can become a focus of attention, with consequent negative conditioning, and persist even after resolution of the depressive episode. In some cases, insomnia may also have an insidious onset without any identifi- able precipitating factor.
The course of insomnia may also be episodic, with recurrent episodes of sleep difficul- ties associated with the occurrence of stressful events. Chronicity rates range from 45% to 75% for follow-ups of 1—7 years. Even when the course of the insomnia has become chronic, there is night—to—night variability in sleep patterns, with an occasional restful night’s sleep interspersed with several nights of poor sleep. The characteristics of insomnia may also change over time. Many individuals with insomnia have a history of ”light” or easily disturbed sleep prior to onset of more persistent sleep problems.
Insomnia complaints are more prevalent among middle-age and older adults. The type of insomnia symptom changes as a function of age, with difficulties initiating sleep being quently among middle-age and older individuals.
Difficulties initiating and maintaining sleep can also occur in children and adolescents, but there are more limited data on prevalence, risk factors, and comorbidity during these developmental phases of the lifespan. Sleep difficulties in childhood can result from con- ditioning factors (e.g., a child who does not learn to fall asleep or return to sleep without the presence of a parent) or from the absence of consistent sleep schedules and bedtime routines. Insomnia in adolescence is often triggered or exacerbated by irregular sleep sched- ules (e.g., phase delay). In both children and adolescents, psychological and medical fac- tors can contribute to insomnia.