How do you know if fatigue is just jet lag?

Timing: Fatigue can be due to the rigors of travel or jet lag. If you are traveling north-south you will not get jet lag. If you have traveled east or west 3 or more time zones you are likely to be jet lagged. Adjust your internal clock to local time by exposure to sunlight and melatonin. East-bound travel is more difficult to adjust to than west-bound travel. Jet lag is worse in the first few days.