Shift work disorder occurs when you have difficulties adjusting to a work schedule that takes place during a time which most people sleep. When you have shift work disorder, there is a conflict between your body’s circadian rhythms and your work schedule. You may have to be at work when your body wants to sleep. Then when you have to sleep, your body expects to be awake.
Jet lag occurs when you travel across multiple time zones and have trouble adjusting to the new schedule. After traveling a long distance by air, your circadian rhythms may still be aligned with the previous time zone. Your body may expect to sleep when it is daytime in the new time zone or be awake when you are supposed to sleep.