Circadian rhythm sleep disorders and phototherapy.

Circadian rhythm sleep disorders are characterized by a desynchronization between the timing of the intrinsic circadian clock and the extrinsic light-dark and social/activity cycles resulting in symptoms of excessive sleepiness and insomnia. This article explores the six recognized circadian rhythm sleep disorders: delayed sleep phase syndrome, advanced sleep phase syndrome, non-24-hour sleep-wake syndrome, irregular sleep-wake pattern, shift work sleep syndrome, and time zone change syndrome. Additionally discussed are the therapeutic roles of synchronizing agents, such as light and melatonin.