The precise medical cause for DSPS is unknown. Circadian rhythms, which regulate the internal biological clock and influence functions such as sleep-wake patterns, are usually described as being out-of-phase in DSPS. If sleep occurs on a continuum, then the circadian rhythms of patients with DSPS signal sleep at delayed intervals.
DSPS often occurs in patients who experience head trauma (e.g., traumatic brain injury [TBI]) or serious illness. In these cases, the body's natural healing process may disrupt normal circadian rhythm and render the biological clock unable to reset or resynchronize.
Lifestyles that allow alternative sleep-wake patterns (e.g., work-at-home jobs, computer programming, artistic careers) may help sustain DSPS, rather than to shape the disorder.