She knows, now, absolutely, hearing the white noise that is London, that Damien’s theory of jet lag is correct: that her mortal soul is leagues behind her, being reeled in on some ghostly umbilical down the vanished wake of the plane that brought her here, hundreds of thousands of feet above the Atlantic. Souls can’t move that quickly, and are left behind, and must be awaited, upon arrival, like lost luggage

— Pattern Recognition by William Gibson

Jet Lag - as the name might imply - is relatively new for humans. Propeller-driven craft or trains often were much slower and didn’t travel as far over between timezones to cause it. Jet-driven airplanes travel such great distances that our circadian rhythm is frequently disrupted - causing disorientation and stress.

Traveling west is usually considered to be an easier shift than east. This is because most humans circadian clock has an endogenous period that’s slightly greater than 24 hours, and it’s easier to expand that window than to shrink it. In most cases, the 6-9 hour shift East causes the most problems.

There’s lots of “cures” for jet lag but in most it boils down to timing and sleep schedules. Push to go to bed at a reasonable bedtime in the target timezone. Time your flight to avoid light when leaving and find light on arrival.

Sometimes, though, you just have to wait for your soul to catch up with your body.