So, my kid and her family were visiting these past 10ish days. They currently live in the Netherlands. They just returned home today, and my daughter was complaining about the Jet Lag. So being the logophile that I am, I had to do my research.

DESYNCHRONOSIS

Desynchronosis is the disruption of biological rhythms caused by either endogenous or exogenous factors. It is a potential cause of many diseases such as cancer, infertility and psychiatric disorders.

Did jet lag exist before planes?
The term "jet lag" is used because before the arrival of passenger jet aircraft, it was uncommon to travel far and fast enough to cause desynchronosis. Travel by propeller-driven aircraft, by ship, or by train was slower and of more limited distance than jet flights, and thus did not contribute widely to the issue.

Jet lag, also called jet lag disorder, is a temporary sleep problem that can affect anyone who quickly travels across several time zones.

Your body has its own internal clock, called circadian rhythms. They signal to your body when to stay awake and when to sleep.

Jet lag occurs because your body's internal clock is synced to your original time zone. It hasn't changed to the time zone of where you've traveled. The more time zones crossed, the more likely you are to experience jet lag.