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Anyone who's flown east or west across several time zones has probably experienced ``jet lag'' -- the fatigue and unusual sleep-wake schedules associated with transcontinental or cross-country flight. These symptoms occur primarily because your internal rhythm is out of phase with the normal temporal environment, creating desynchronization and resulting in sleep deprivation.
If your system says it's 3:00 a.m., but local time is 12:00 noon, you may find yourself falling asleep at lunch. Conversely, if the local time is midnight and your biological time is 10:00 a.m., you'll have a hard time falling asleep.
A large part of combating jet lag is knowing its causes and being prepared to deal with it. The following discussion explains some of the reasons why we have jet lag, and how to deal with it on your next trip.
What causes jet lag?
The symptoms of jet lag include fatigue, disorientation, decreased concentration and performance, disruption of appetite, insomnia, excessive sleepiness and muscle aches. This raft of symptoms is caused by the desynchronization that occurs when you rapidly travel to a place in a different time zone. That's why the effect is called jet lag: You won't get it on a long, slow, confining journey, such as on a bus or ocean liner.
In addition, traveling due north or south, without crossing time zones, won't give you jet lag. For example, a 12-hour flight from New York to Lima (no time difference) will have about the same effect on you as a 12-hour car ride -- no jet lag, but normal fatigue from sitting in the same place for half a day. Not only that, but if you were to fly completely around the globe in 8 hours and land at your point of departure, you wouldn't have jet lag at all!
Accordingly, the number, rate and direction of time-zone changes are the most important factors in determining jet-lag symptoms. A 2-hour flight from New York to Chicago, resulting in a 1-hour time change, is less disruptive than a 7-hour flight from New York to London (5-hour difference). A 12-hour flight from Copenhagen to Tokyo over the Arctic Circle, passing through many time zones,...