Circadian rhythm

A person’s circadian rhythm, popularly known as one’s “body clock,” is the pattern that each of us sets up for governing our routine of working, eating and sleeping through a 24–hour period. Most of us aren’t even aware of the degree to which we have routinized our lives, until we dislocate the rhythm by taking an overnight flight to Europe or the Orient with little or no sleep en route. When we try to conduct our normal activities on the day we arrive, the resulting mental and physical dislocation can be severe. Because this phenomenon was almost unknown until air traffic entered the jet age, it is often referred to as “jet lag.” Circadian is derived from the Latin words circa (about) and dies (day).