Delayed Sleep Phase Disorder

Symptoms: Stable sleep schedule that is substantially later than the conventional or desired time. Patients with DSPD have sleep onset insomnia and extreme difficulty arising when they attempt to conform to a conventional daytime schedule

Etiology and affected groups: May arise from longer-than-average circadian period, reduced exposure to light during morning hours. DSPD is most common during adolescence and may be self-reinforced

People with this disorder are called "Night owls". I am one :S