circadian rhythm sleep disorder

n. A sleep disorder caused by a mismatch between a person's circadian rhythm and the demands of the world around her/him resulting in the person's feeling sleepy when he/she should be awake and feeling energetic when he/she should be sleeping. In the delayed sleep-phase type the person's circadian rhythm is longer than 24 hours so he/ she has difficulty falling asleep and waking up as early as required. In the jet-lag type a person's circadian rhythm is appropriate for a different time zone, causing him or her to want to be awake and asleep at inappropriate local times. In the shift-work type repeated changes in work shift result in a mismatch between sleep/work schedule and bodily clock; this is usually worse when change in work schedule moves from later to earlier, as opposed to earlier to later. Most people cope better with waking and sleeping at later times than they do at earlier times.