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Delayed sleep-phase syndrome (DSPS), also known as delayed sleep-phase disorder (DSPD) or delayed sleep-phase type (DSPT), is a circadian rhythm sleep disorder, a chronic disorder of the timing of sleep, peak period of alertness, core body temperature, hormonal and other daily rhythms relative to the usual norms. People with DSPS tend to fall asleep some hours after midnight and have difficulty waking up in the morning.

Often, people with the disorder report that they cannot sleep until early morning, but they fall asleep at about the same time every "night", no matter what time they go to bed. Unless they have another sleep disorder such as sleep apnea in addition to DSPS, patients can sleep well and have a normal need for sleep. Therefore, they find it very difficult to wake up in time for a typical school or work day. If, however, they are allowed to follow their own schedule, e.g. sleeping from 4 a.m. to noon, they sleep soundly, awaken spontaneously, and do not feel sleepy again until their next "night".

The syndrome usually develops in early childhood or adolescence, and sometimes disappears in adolescence or early adulthood. It can be to a greater or lesser degree treatable depending on the severity, but has not yet been found to be fully curable. Prevalence among adults, equally distributed among women and men, is approximately 0.15% or three in 2000 (see below).

DSPS was first formally described in 1981 by Dr. Elliot D. Weitzman and others at Montefiore Medical Center. It is responsible for 7–10% of cases where patients complain of chronic insomnia. However, as few doctors are aware of its existence, it often goes untreated or is treated inappropriately. DSPS is frequently misdiagnosed as primary insomnia or as a psychiatric condition.

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I think I have this either that or I am just stupid for staying up late