Jet lag feels like exhaustion, so people try to fix it by sleeping. That mostly does not work, and the reason is that jet lag is not a tiredness problem. It is a timing problem: your internal clock still runs on the city you left, while the sun, your meals and your meetings run on the city you arrived in. Until those agree, you feel wrong at every hour.
Get that framing right and the fix becomes obvious. You are not trying to rest. You are trying to move a clock — fast, and in the correct direction.
Why direction decides everything
Your internal clock naturally runs slightly longer than 24 hours. That single fact explains the most important asymmetry in jet lag.
Flying west asks you to stay up later and wake later — to lengthen your day. Your clock already drifts that way, so this is the easy direction. You will usually adjust roughly a day per time zone, sometimes faster.
Flying east asks you to go to sleep earlier and wake earlier — to shorten your day, and to fall asleep when your body thinks it is still evening. This fights your natural drift, and it is markedly harder. Eastward adjustment often takes longer than a day per zone.
So the same six-hour shift is two different problems. Knowing which one you are solving determines everything you do with light — which is the actual tool.
Light is the lever
Light is by far the most powerful input to your body clock, which makes it the most powerful tool for moving it. But the timing is not just important, it is directional — the same light will drag your clock earlier or push it later depending on when your body thinks it is.
The rule:
- Light in your body's morning shifts your clock earlier (advances it). This is what you want going east.
- Light in your body's evening shifts your clock later (delays it). This is what you want going west.
Get the timing wrong and you actively push your clock the wrong way and prolong the misery. So the two cases are genuinely different protocols, not one piece of generic advice.
Flying east (the hard way)
You need to advance your clock — get sleepy earlier. So seek morning light at the destination and avoid late-evening light.
- On arrival, get bright morning light — outdoors is best by a wide margin.
- In the first day or two, be cautious with light in the early morning if the shift is large; very early light can hit the wrong side of your clock and delay it. As you adjust, morning light becomes unambiguously helpful.
- Dim the evenings. Sunglasses on the flight and late in the day can help you avoid the delaying signal.
- A short, correctly-timed dose of melatonin in the destination evening can nudge the advance. Keep it low-dose and treat it as a timing cue, not a sleeping pill — and check with a pharmacist or doctor about your specifics.
Flying west (the easy way)
You need to delay your clock — stay up later. So seek evening light and get light later in the day.
- Push to stay awake until a reasonable local bedtime. Evening light is working with your natural drift here.
- Get outside in the afternoon and evening at the destination.
- Resist the urge to crash on arrival at 4pm — a nap that long at that hour will wreck the following night.
Before you even fly
You can pre-load the adjustment and cut days off the recovery.
Shift your schedule a few days early. For an eastward trip, go to bed and wake 30–60 minutes earlier each day for two or three days before departure. For westward, do the reverse. Even a partial pre-shift means you land with less of a gap to close.
Set your watch to the destination on boarding and start acting on that time — when you sleep, when you eat. The mental switch matters more than it sounds.
The supporting cast
Light does most of the work. These help it.
Meal timing. Your gut has its own clock, and eating on destination time helps drag your system into line. Try to eat meals at local mealtimes even before you feel hungry.
Strategic caffeine. Useful to hold the line — caffeine in the destination morning to stay awake and reinforce the new schedule. Just keep it well clear of destination bedtime, or you trade jet lag for a caffeine-fragmented night. (Why the cutoff still applies.)
Naps, carefully. A short nap under 30 minutes can get you through a rough afternoon without denting the coming night. A three-hour crash will reset you backward. Keep them short and early.
Hydration and movement. Long flights are dehydrating, which amplifies the fatigue and muddies your read on your actual clock state. Water, and moving around the cabin, both help.
For the underlying machinery — how the clock is set and re-set — The Natural Sleep Lab's primer on circadian rhythm is a good companion, and the same morning-light principles that anchor an ordinary day are what you are deploying, just re-timed.
Protect the sleep you do get
Jet lag fragments sleep even once the timing starts to align — strange room, strange noises, a clock still halfway between zones. Anything that improves the quality of the sleep you manage to get is worth more than usual while you are adjusting. Nasal breathing keeps sleep deeper and less fragmented, and a strip of Titan Recovery's bamboo silk mouth tape travels well for exactly that. (What changes across a night.)
And once you are adjusted, the thing that keeps you adjusted is the same one that runs an ordinary week: a consistent wake time, anchored with morning light. (Why wake time is the lever.)
The bottom line
Jet lag is a timing mismatch, not tiredness, so you fix it by moving your clock rather than resting. Flying west is easy because it lengthens your day, the direction your clock already drifts; flying east is hard because it shortens it. Use light directionally — morning light to shift earlier going east, evening light to shift later going west — and pre-shift your schedule a few days before departure.
Eat on local time, use caffeine to hold mornings, keep naps short and early, and protect the fragmented sleep you do get. Roughly a day per time zone going west, longer going east — and light, correctly timed, is what shortens it.