Jet Lag
	The human body is attuned to a roughly 24-hour rhythm, with the sun rising and setting on a fixed schedule and sleep taking place at a certain time during that cycle. When a person crosses several time zones, his or her body must grow accustomed to the new time zone's schedule of light and darkness. Until that adjustment occurs, sleep is fitful and the person awakens or feels sleepy at odd hours. If the stay in a new time zone is to be short (a day or two), some specialists recommend that the traveler try to go to sleep and get up according to what time it is back home. For longer journeys, some people begin several days in advance to gradually alter their meals and activities, hoping that by the time they arrive they will experience little disruption. They may even try to trick their bodies into believing the new day-night schedule is already in effect by turning on bright lights at night and pulling down blinds during the day or by matching their meals to the appropriate hours in their destination time zone. Medications can sometimes be helpful for getting to sleep in a new time zone, when the clock says it's bed-time but the body, "set" for the old time zone, feels awake.
	Irregular Sleep-Wake Schedule
	Some people continually alter their sleeping schedules so dramatically that they constantly feel tired or uncomfortable. A job requiring repeated awakenings - a doctor on call for 48 hours straight, for example - can severely alter the normal sleep-wake cycle. Freelance writers and artists often set their own erratic schedules. Eventually, such irregular cycles may snowball into serious problems of falling asleep, staying asleep, or remaining alert during periods of work or social activity. People who work rotating shifts - such as nurses, police officers, mariners and transportation workers, to name a few - may have little control over their sleep schedules. Irregular sleep-wake cycles may contribute to increased industrial accidents among people who rotate from shift to shift frequently. Studies show that shift work is not so troublesome when the changes take place after long intervals; when shift changes proceed clockwise (that is, moving from the evening shift to the night shift, to the day shift); and when time off accompanies shift changes. Effective treatment for an irregular sleep-wake cycle requires that the individual maintain a strict sleep-wake schedule under professional supervision. With the person's full cooperation, the problem is often resolved within days or weeks. For the person who can't fully control his or her work schedule, the sleep specialist will try to devise more innovative approaches, but sometimes the problem can't be resolved without returning to regular work hours.
	Delayed Sleep Phase Syndrome
	Some people can't (or won't) go to sleep until well past conventional bedtime hours - perhaps 3 or 4 A.M. If their jobs or home environments permit them to sleep correspondingly late, these "night people" may go through life with no problems other than minor scheduling difficulties. But when a circumstance requires that they assume a conventional schedule, they may find it difficult to fall asleep and virtually impossible to get up earlier. One technique sleep specialists use to reset the body's clock is as follows: The person is told to choose an appropriate new bedtime - for example, midnight. He or she should sleep, or try to sleep, for five hours only. A few days of this firm, five-hour schedule and the person will be sleepy most of the time. Then he or she should increase the sleep time by 15 minutes - the person should get up at 5:15 A.M. Every few days another 15 minutes should be added, until the sleep cycle has been extended to its normal length, at new hours. The technique requires persistence and motivation and may be easiest to accomplish with professional supervision. People must be persistent in adhering to the new schedule to avoid slipping back into the old pattern.