Jet lag throws people’s internal clocks off, their bodies thinking they are home (or wherever they were), but the outside environment saying they are somewhere else (wherever they are).
But that’s kind of a “duh” statement, being pretty much a definition of the “lag” part.
But, since it’s a serious part of travel in today’s world, what can be done to counteract the lagging? You are in luck, because we have answers here!