Why it happens
Your internal clock is set by the sun where you came from. Fly across time zones and it's suddenly out of sync with local day and night — so you're wired at 2 am and exhausted at noon. Recovery runs at roughly one day per time zone crossed, and flying east is harder than flying west because advancing the clock is tougher than delaying it.
Light is the master switch
Light is the strongest signal for your body clock. The rule of thumb:
- Flying east (e.g. US → Europe): seek morning light at your destination and avoid bright light late.
- Flying west (e.g. Europe → US): get evening light and avoid early-morning light.
Shift your sleep, don't fight it
- Switch to the destination's schedule the moment you board.
- On arrival, stay up until a normal local bedtime even if you're shattered.
- Avoid long daytime naps — keep any nap to about 20 minutes.
- Plan local bedtimes ahead with the sleep cycle calculator.
Use caffeine on purpose
Caffeine is a tool here, not a habit: a coffee in the destination's morning helps you stay awake and lock onto local time. The catch is the same as always — stop early enough that it doesn't sabotage the night's sleep you're rebuilding. Check what's left at your new bedtime with the half-life calculator.
Put it into practice: set your destination bedtimes with the sleep calculator and your caffeine cutoff with the half-life calculator.