Sleep schedule disorders typically arise from behaviors that misalign the natural sleep-wake schedule embedded in the brain, with the "existing schedule" which often conflict with social, environmental and work needs.
This disorder is more common nowadays in specific populations:
Those working night shifts and trying to reconcile with daytime house responsibilities on days off from work.
Those whose jobs require frequent travel in different time zones.
Those who work in rotating shifts or at jobs with frequent changes in time shifts.
Those who live a distance away from work and require long daily commutes and have to start an early shift.
Young people who frequently stay up late and awaken early for school with different schedules on weekends.
Old people who go to sleep early an awaken in the middle of the night and unable to return to sleep (frequently taking small naps during the day).
The fatigue and somnolence that result from these disorders accumulates in a subtle way, until it finally interferes with performance of daily activities. All these disorders need realignment (of sleep) through the use of sleep logs and other interventions.
Other sleep disorders that may need special attention include:
Restless Legs Syndrome
Post-Traumatic Stress Disorder (PTSD) associated nightmare
Narcolepsy with daytime sleepiness