Jet-Lag is something when you have finished traveling and you have entered into a new timezone and you get off the plane and you feel all queazy and tired.
Have you not ever heard anyone say "Have you got jet-lag?"
More technically, it is when you travel from one time zone to another, and your body is still running on the old time zone when you get to the new one. Therefore you may feel tired at weird times of the day. When you travel quickly across time zones (for example across the Atlantic) you don't have enough time to adjust to the new time zone (you are moving so quickly) so your biological clock is still running on the old time, and you feel drowsy and icky for a couple of days. It's almost like you have to "catch up" to the new time. After about 3 days (depends on the person) in the new time zone your body adapts to the new time and the "jet-lag" (the term for the lousy condition you are in) goes away.
The difference between the time zones has to be somewhat significant (6+ hours) for you to experience real jet-lag. I think the bigger the difference between the time zones, the more jet-lag you experience (or the worse it feels).
The best way to get over jet lag is to try to force yourself to be in the time zone you are entering.
For instance, going from NYC to London. London is 5 or 6 hours ahead of NYC. If taking an evening flight, it's better to try to sleep/rest on the plane if possible rather than stay up. By the time we landed, it was 2AM in NYC, but 8AM in London. I took an hour nap at the hotel before trying to push through the rest of the day to a 'normal' bed time in London time. Since I don't sleep well on planes, I probably only had 3 hours sleep that 1st day in London.
There are certain vitamins and such that people claim will help jet lag. Also, I find keeping hydrated is important. My eyes get really dry on long plane rides and that contributes to feeling tired.
Brian Boitano said that massaging certain places on the body (I think it was the temples and I can't remember if there was another place) helps with that as well... don't know if it's true... I'm always either asleep or just trying to keep my cookies!
I only have to deal with a 3 hour difference on a trip to CA and I don't feel good until about 5-6 days into the trip. Since my trips are only a week, I only get 2 really normal feeling days. Then I have to do the return trip back and I'm still messed up for another 5-6 days. I just don't travel to new time zones very well. DST is even a huge challenge for me. :\
Unless this has something to do with the skaters, who I am sure experience jet-lag from time to time with all their travels, shouldn't this topic be in LeCafe?
I think the question originally came up with respect to the Cup of China. Skaters attending from North America had to compete at times which, to their biological clocks, were like 3 in the morning. From the scores, it soundied like everybody did really badly, so the conjecture was that jet lag might have had something to do with it.