Insomnia Disorder 365
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 symp toms. 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 mo st frequently observed as a comorbid con-
dition with another medical condition or ment al disorder. For instance, 40%–50% of indi-
viduals with insomnia also present with a comorbid mental disorder. 
Development and Course
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 onse t 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 sl eep disturbances, in-
somnia may persist long after the initial trigge ring event, possibly because of conditioning
factors and heightened arousal. The factors that precipitate insomnia may differ from
those that perpetuate it. For example, an in dividual who is bedridden with a painful injury
and has difficulty sleeping may then develop negative associations for sleep. Conditioned