http://www.sleepfoundation.org/site/c.huIXKjM0IxF/b.2418909/k.C148/Jet_Lag.htm
Jet lag, one of the 84 known or suspected sleep disorders that affects millions of people each year, occurs when the body's biological clock is out of sync with local time. When traveling to a new time zone, our bodies are slow to adjust and we feel excessively sleepy during the day or wide awake at night. This document provides a general overview on jet lag, along with treatment and coping strategies.