Because eastward demands the harder direction: your circadian clock runs slightly long on its own, so it delays easily (westward) and advances reluctantly (eastward) - mathematical modeling formalizes it: delays are self-enhancing, advances fight the oscillator.
Recovery data confirm westward trips resolve faster than equal eastward ones. Counter-moves: morning light at destination advances the clock, avoid bright evening light early on, pre-shift sleep 30 to 60 minutes earlier, and melatonin (0.5 to 1 mg) in the early destination evening is the best-evidenced assist. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper .
What to do
Common questions
Why do I get jet lag worse going east?
Because eastward travel demands the harder direction of clock surgery. Your circadian rhythm, left to itself, runs slightly long - past 24 hours - which means it drifts later (delay) easily and pulls earlier (advance) reluctantly. Flying west asks for a delay: stay up later, sleep in - your body cooperates. Flying east demands an advance: sleep before you are sleepy, wake at what your body insists is 4 AM. Mathematical modeling of the circadian pacemaker formalizes the asymmetry: delays are self-enhancing - each step later makes the next easier - while advances fight the oscillator's natural dynamics, and recovery data confirm westward trips resolve faster than eastward ones of the same size. The practical counter-moves for eastbound: light is the lever - get bright morning light at your destination (it advances the clock) and avoid bright evening light the first days (it delays you backward); shift your sleep schedule 30 to 60 minutes earlier for a few nights pre-flight; and consider arriving in the afternoon, since morning arrivals hand you light that shifts you the wrong way. Melatonin in the early destination evening (tiny dose, 0.5 to 1 mg) is the best-evidenced chemical assist for the eastward advance.