Delayed sleep phase syndrome (DSPS), sometimes called phase lag syndrome, is a sleep disorder of circadian rhythm. However, unlike jet lag, and the effects of shift work, delayed sleep phase syndrome is a persistent disorder. In fact, in clinical settings, it is, perhaps, the most commonly seen complication of sleep-wake patterns.

Delayed sleep phase syndrome results from a disturbance between the patient’s internal biological clock and the external environment. Again, unlike jet lag, this desynchronization is not activated by travel or change in external environment. Rather, the patient’s propensity to fall asleep is simply “delayed” in relation to that of the general public. Subsequently, a patient who is experiencing DSPS is out of phase with the routine that governs most of his or her life.

A person with this disorder is typically unable to fall asleep before 2 a.m. and has great difficulty waking early, say by 7 a.m. These people are sometimes called "night owls" or described as "not being morning people." If allowed to sleep a full seven to eight hours, i.e. until 10 a.m., they feel rested and function normally. Unfortunately, this is not usually the case.

The main difficulty for a person with DSPS is meeting the expectations of society, i.e. functioning early for school or work. A person with DSPS may lose jobs or fail courses in school. So, this syndrome affects individuals on a social level at the same time that it compromises their health and hygiene.

Patients with DSPS may initially refer to their symptoms as insomnia. Again, the significance that society places on traditional sleep-wake patterns usually dictates what is normal. And as soon as people deviate from a normal sleep pattern, they tend to assume they are not capable of sleep at all. But this is not true. Patients who suffer from DSPS are able to get plentiful sleep; it’s just postponed. If they can sleep until they are ready to wake, patients with DSPS can experience rewarding sleep. The reality is that DSPS usually makes it hard to wake up, as the patient simultaneously indulges his or her late night sleep routine and yields to the wake routine of society.

Diagnosis is based on sleep history, and treatment ranges from learning to respond differently to external indicators of sleep-wake time to practicing new and proper sleep habits.

Incidence
The exact incidence of delayed sleep phase syndrome is unknown. In one recent study, DSPS accounted for 40 percent of disorders involving sleep-wake schedules among 5000 participants. It is estimated to affect 7 percent of teenagers and to be the cause in 10 percent of chronic insomnia cases. Although DSPS usually surfaces in childhood, it is seen most frequently in young adults, especially men, which suggests a concurrence with lifestyle.