Jet lag is caused by flying in an airplane and crossing one or more time zones, such as traveling east to west or west to east. Crossing time zones disrupts the body's biological "clock," or 24-hour rhythms (circadian rhythms). Sleep patterns are one of these rhythms. Jet travel across time zones may make it hard for you to fall asleep or stay asleep at night and stay awake during the day. Jet lag also can cause fatigue, irritability, and indigestion.

The symptoms of jet lag may take from one to several days to go away. Jet lag usually lasts longer when you fly east than when you fly west.

Melatonin is a hormone the body makes that regulates the cycle of sleeping and waking. It is not known if taking melatonin to help "reset" your sleep and wake cycle helps with jet lag.

There are other things you can do to decrease the effects of jet lag. Be rested before you leave, and try to walk around during the flight so that you are not confined to cramped spaces for long periods of time. Do not drink alcohol, but drink lots of water, because the air in airplanes tends to be dry. Vitamins and herbal remedies that can be bought without a prescription can also be tried to help reduce jet lag. Going outdoors during the day may help fight jet lag by resetting your circadian rhythm.