Delaye 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 societal norms. People with DSPS tend to fall asleep well after midnight and have difficulty waking up in the morning.