early awakening, and exposure to light in th e early morning should be considered, partic-
ularly in older adults . Careful attention should be paid to rule out other sleep-wake dis-
orders, such as insomnia disorder, and other mental disorders and medical conditions that
can cause early morning awakening. 
Depressive and bipolar disorders. Because early morning awaken ing, fatigue, and sleep-
iness are prominent features of major depres sive disorder, depressive and bipolar disor-
ders must also be considered. 
Comorbidity
Medical conditions and mental disorders wi th the symptom of early morning awakening,
such as insomnia, can co-occur with the advance sleep phase type. 
Irregular Sleep-Wake Type
Diagnostic Features
The diagnosis of irregular sleep-wake type is based primarily on a history of symptoms of
insomnia at night (during the usual sleep pe riod) and excessive sleepiness (napping) dur-
ing the day. Irregular sleep-wake type is char acterized by a lack of discernable sleep-wake