What causes jet lag
Jet lag occurs when your circadian rhythm — the internal clock governing sleep, hunger, and hormone release — is out of sync with the local time at your destination. The body adjusts at roughly one to one-and-a-half time zones per day, so crossing six zones can mean four to six days of disrupted sleep and energy.
Eastward travel is generally harder because it requires advancing the body clock, which is more difficult than delaying it. Symptoms include fatigue, insomnia, digestive issues, difficulty concentrating, and general malaise.