About a week ago we returned from Russia. Moscow is nearly half way around the world from the west coast of the U.S. - eleven time zones away to be precise. When we arrived home in CA we were seriously jet lagged, our sleep/wake/eat cycles were truly screwed up. We were awakening at 2 a.m. and practically passing out in mid afternoon. Those cycles aren't entirely settled down yet.
The other DrC, my wife and traveling companion of 36 years, has a rule of thumb concerning jet lag. She believes that for every time zone your cross in an airplane flight, you need a day to get readjusted. For example, if you fly from the East Coast to the West Coast you cross three time zones and need three days to get over the resulting jet lag.
Gentle readers, I would be interested in your experiences with jet lag.