Sleep and Jet Lag

Jet lag happens because your circadian rhythm stays set to your departure time zone for days after you arrive. As a rough rule, it takes about one day per time zone crossed to fully adjust — though light exposure can speed this up considerably.

Travelling east (losing time) is harder to adjust to than travelling west, because it requires your body clock to shift earlier, which it resists more than shifting later.

Seek bright light in the morning at your destination if you've travelled east, and avoid it if you've travelled west (where evening light helps instead). A few days before departure, gradually shifting your sleep and meal times toward the destination time zone reduces the adjustment needed on arrival.

Melatonin, taken at the target bedtime for the first few nights, is one of the better-evidenced jet lag aids — but light exposure timing remains the single most powerful tool, and it's free.