Such people often cannot hold day shift jobs and gravitate toward evening shifts. The pattern of delayed sleep often develops early in life, when demands of academic and social obligations increase. Adolescents and college students are particularly vulnerable. Some people successfully re-entrain their schedules to societal norms. Unlike other insomnia syndromes, DSPS features normal sleep provided there is opportunity to sleep late.
Studies demonstrate that the temporal sequence and proportion of sleep stages are normal.
The severity of DSPS depends upon how rigidly the patient must adhere to a conventional schedule. This has obvious implications for safety and productivity. Moreover, some patients may use sleeping pills or alcohol to manipulate their nighttime sleep schedules. Usually, patients with other types of insomnia report some sleep maintenance difficulty with middle-period arousals, while DSPS patients report no intrinsic sleep problems provided they observe their own schedules. For some people, motivational problems may account for sleep phase delay.