Delayed sleep phase disorder is a circadian rhythm sleep disorder. It affects the timing of sleep. It has an effect on the time when a person is most alert during the day. It also affects core body temperature rhythm and other daily rhythms. People with DSPD generally fall asleep after midnight. They have difficulty waking up in the morning. Affected people usually have normal need for sleep. This condition usually develops in childhood or adolescence. DSPD is a life-long condition.