Delayed sleep phase disorder

Delayed sleep-phase disorder (DSPD), also known as delayed sleep-phase syndrome (DSPS) or delayed sleep-phase type (DSPT), and in the 2014 revision of the International Classification of Sleep Disorders (ISCD-3), delayed sleep-wake phase disorder, is a chronic dysregulation of a person's circadian rhythm (biological clock), compared to the general population and relative to societal norms. The disorder affects the timing of sleep, peak period of alertness, the core body temperature rhythm, hormonal and other daily cycles. People with DSPD generally fall asleep some hours after midnight and have difficulty waking up in the morning. People with DSPD probably have a circadian period significantly longer than 24 hours. Depending on the severity, the symptoms can be managed to a greater or lesser degree, but there is no known cure.