Jet lag is caused by an upset in the body's biological what?

Jet lagis also known as

time zone change syndromeor

desynchronosis. Jet lag can occur when people travel rapidly from east to west, or west to east on a jet plane. It is a physiological condition which upsets our body's circadian rhythms - hence, it is classified as a circadian rhythm disorder. Jet lag symptoms tend to be more severe when the person travels from westward compared to eastward.