Why crossing time zones wrecks your sleep, and a practical 48-hour plan to land sharp instead of foggy.
Jet lag is not just tiredness: it is your internal clock pointing at the wrong time zone. Your body runs on a roughly 24-hour circadian rhythm tuned by light. Fly across several zones and that clock lags behind, which is why the first two nights are the hardest.
Eastward is harder than westward
Flying east (e.g. US → Europe) shortens your day, forcing your clock earlier, the direction it resists most. Flying west lengthens the day, which is easier to absorb. A rough rule: budget about one day of recovery per time zone crossed.
Know the gap before you fly
Set your destination clock the moment you board, and start living on it. Seeing both times side by side makes "should I sleep now?" obvious:
A 48-hour light & sleep plan
Light is the strongest lever. Seek it or avoid it at the right hours and your clock shifts faster. This plan adapts to your specific flight:
Paris → Tokyo
出発前の睡眠シフト
- 東向きは大変：1日が短くなります。
- 数日前から毎日約1時間早く就寝・起床。
- 到着後は朝の強い光を浴び、夜遅い光を避ける。
- 昼寝は15時前に短く。到着日は外に出ましょう。
Pack so arrival is painless
| Carry-on essential | Why |
|---|---|
| Refillable water bottle | Cabin air is desert-dry; dehydration mimics jet lag. |
| Eye mask + earplugs | Control light and noise to nap on destination time. |
| One change of clothes | If bags are delayed, you still feel human. |
Double-check what you can actually bring on board before you pack:
| 航空会社 | 機内 | 預け |
|---|---|---|
| IATA guideline | 7 kg, 55x40x20 cm | 23 kg, 158 cm total |
| Emirates (Economy) | 7 kg | 30 kg |
| ANA (Economy) | 10 kg | 23 kg x 2 |
| Delta (Economy) | 1 bag + personal item | 23 kg (fee) |
目安です。必ず航空会社に確認を。
On the plane
- Set your watch to the destination immediately.
- Skip the "free" alcohol: it fragments sleep.
- Walk the aisle hourly; move your ankles often.
- Eat on the destination's meal schedule when you can.
Land, get outside into daylight, and resist the 4 p.m. nap. You'll be on local time by day two, ready for the itinerary you built in voyageons.
Search questions answered
Readers asking “how long does jet lag last,” whether a short flight can cause it, or what recovery looks like from the USA to the UK will find the practical timeline here: symptoms often improve over several days, but the exact duration depends on time zones, direction and sleep timing.
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