December 2020 | Reviewed by: Virginia Skiba, MD and Reeba Mathew, MD
What is non-24-hour sleep-wake rhythm disorder?
Non-24-hour sleep-wake rhythm disorder (N24SWD) is one of several circadian rhythm disorders. People with these disorders have sleep times that seem to be out of alignment. Their sleep patterns do not follow the “normal” sleep times at night.
The sleep time of people who have N24SWD shifts a little later every day. Sleep time and wake up time continue to move later and later every day. Sleep times go in and out of alignment with other people as weeks go by.
Normal people have a circadian rhythm that is slightly longer than 24 hours. Every day, morning light and other behaviors reset the sleep-wake clock to a 24-hour schedule. Without light and this clock resetting, people’s sleep time will drift later and later. This is why many people who are blind have N24SWD. Light is the major influence on resetting the brain’s clock.
As your sleep pattern drifts a little later every day, N24SWD can be confused with other circadian rhythm disorders. As sleep time drifts later, you do not fall asleep until morning. It may seem like you have delayed sleep-wake phase. After days of later and later bedtime, you are sleeping during the day. After more days, you begin to sleep in the early afternoon and evening. This makes it look like you have advanced sleep-wake phase. After more days, you are back to sleeping during normal night hours. Then the drifting sleep time continues around the clock again. The sleep time is not broken up into pieces as with irregular sleep-wake rhythm. The sleep time is only broken if there are outside disturbances. Your main sleep time does not occur at the same time every day. It continues to get later and later every day.