Free Running Cycle

A person's circadian rhythm is a 24-hour cycle that usually relies on external cues (such as when the sun goes up or down). A person's free-running cycle, or free-running rhythm, is his or her daily sleep cycle that does not depend on these external cues. As a result, a person who is on a free-running cycle may experience unusual sleep schedules causing insomnia or daytime sleepiness. Blind people who do not rely on the sun to guide their circadian rhythm often experience free-running cycles.