Table 1.

International Classification of Sleep Disorders categories of Circadian Rhythm Sleep Disorders with typical clinical features.

Disorder	Clinical features
Delayed sleep phase type	Sleep and wake times are delayed (later) compared to normal individuals and desired times, with striking inability to fall asleep and wake earlier at the desired time
Advanced sleep phase type	Sleep and wake times advanced (earlier) compared to normal individuals and desired times, with striking inability to remain awake and remain asleep until the desired time
Irregular sleep-wake type	Unrecognizable pattern and disorganized sleep and wake times, with insomnia and/or excessive daytime sleepiness
Free running type	Gradually delayed bedtime by 1-2 hours a day with insomnia and inability to wake in the morning
Jet lag type	Inability to fall asleep and wake at times compatible with desired times due to recent travel to new time zone.
Shift work type	Inability to fall sleep (during the day) and remain awake (at night) at times required for work schedule.