372 Sleep-Wake Disorders
related sleep disorders are suggested by a hist ory of loud snoring, pauses in breathing
during sleep, brain injury, or cardiovascular disease and by the presence of obesity, oro-
pharyngeal anatomical abnormalities, hyperten sion, or heart failure on physical examina-
tion. Polysomnographic studies can confirm the presence of apneic events in breathing-
related sleep disorder (and their ab sence in hypersomnolence disorder).
Circadian rhythm sleep-wake disorders. Circadian rhythm sleep-wake disorders are
often characterized by daytime sleepiness. A  history of an abnormal sleep-wake schedule
(with shifted or irregular hours) is present in individuals with a circadian rhythm sleep-
wake disorder. 
Parasomnias. Parasomnias rarely produce the prol onged, undisturbed nocturnal sleep
or daytime sleepiness characterist ic of hypersomnolence disorder.
Other mental disorders. Hypersomnolence disorder must be distinguished from mental
disorders that include hypersomnolence as an essential or associated fe ature. In particular,
complaints of daytime sleepiness may occur in a major depressive  episode, with atypical fea-
tures, and in the depressed phase of bipolar di sorder. Assessment for ot her mental disorders is
essential before a diagnosis of hypersomnolence disorder is co nsidered. A diagnosis of hyper-
somnolence disorder can be made in the presence  of another current or past mental disorder. 
Comorbidity
Hypersomnolence can be associated with depressive disorders, bipolar disorders (during a
depressive episode), and major depressive disorder, with seas onal pattern. Many individu-
als with hypersomnolence disorder have symptoms  of depression that may meet criteria for