Jet lag refers to a variety of unpleasant symptoms that afflict
most individuals for several days after traveling rapidly
through several time zones. Typical symptoms include daytime
sleepiness, fatigue, impaired alertness, and trouble initiating
and maintaining sleep. The disturbance is thought to arise from
the failure of the internal biological clock to adjust quickly
to phase shifts in the external environment—in particular, the
light-dark cycle—at the flight destination (1, 2). Beyond the
circadian rhythm factor, stresses of travel preparation and
sleep deprivation associated with the flight can contribute to
jet lag. Although jet lag typically lasts only a few days, its
symptoms can be quite disruptive, impairing work performance (1,
3, 4) or interfering with vacation activities. The severity of
jet lag is related to the number of time zones traveled, with
the effects generally worse for eastward travel (5, 6). To our
knowledge, the prevalence of jet lag and the relative frequency
of various jet lag sym