When flying from one time zone to another, many travelers dread dealing with jet lag. The ]]>Centers for Disease Control and Prevention (CDC)]]> states that “jet lag results from the slow adjustment of the body clock to the destination time, so that daily rhythms and the internal drive for sleep and wakefulness are out of synchrony with the new environment.” Jet lag does not happen to everyone who flies—it becomes more of a problem when the traveler passes through three or more time zones.
How jet lag affects a person depends on where she travels to. The CDC notes that if a person is traveling to an eastern destination, she can have trouble falling asleep at night and waking up the next morning; the duration of the jet lag is two-thirds times the number of zones she traveled through. For example, if she goes through six time zones during her flight, her jet lag will last four days. If a person is traveling to a western destination, she will be sleepier sooner in the evening and wake up much earlier than usual; the duration of the jet lag is half of the number of zones she traveled through, according to the CDC. Therefore, if this traveler also goes through six time zones, but westward bound, her jet lag will last three days.