<unk>  <unk> , also known as<unk><unk> -phase disorder or as circadian rhythm<unk>  disorder<unk><unk> -phase type (DSPT), is a chronic disorder of<unk>  timing. People with<unk>  tend to fall<unk>  at very late times, and also have difficulty waking up in the morning.
Often, people with the disorder report that they cannot<unk>  until early morning, but they fall<unk>  at about the same time every "night", no matter what time they go to bed. Unless they have another<unk>  disorder such as<unk>  apnea in addition to<unk> , patients can<unk>  well, and have a normal need for<unk> . Therefore, they find it very difficult to wake up in time for a typical school or work day if they have only<unk> t for a few hours. However, they<unk>  soundly, wake up spontaneously, and do not feel<unk> y again until their next "night" if they are allowed to follow their own late schedule, e.g.<unk> ing from 4 a.m. to noon.
The<unk>  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, but cannot be cured.<unk>  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 of chronic insomnia. However, as few doctors are aware of its existence, it often goes untreated or is treated inappropriately.<unk>  is often frequently misdiagnosed as primary insomnia or as a psychiatric condition.
Delayed sleep phase syndrome
Advanced sleep phase syndrome
Circadian rhythm sleep disorder
Non-24-hour sleep-wake syndrome
Non-rapid eye movement sleep arousal disorder
Shift work sleep disorder
Nightmare disorder
Sleep hyperhidrosis