If you have plans to take a long trip that involves flying across several time zones, you already may be dreading that exhausted, sleepless, irritable feeling that results when your body is forced to reset its internal rhythms. Jet lag, also known as desynchronosis, can cause insomnia, daytime sleepiness, loss of concentration and alertness, fatigue, irritability, disorientation, depression and gastrointestinal ills [source: Eastman and Burgess]. Unfortunately, it afflicts almost everybody. A 1998 study found that 94 percent of Americans who fly long distances suffered from jet lag, and 45 percent considered their symptoms severe [source: James].

Jet lag makes many of us miserable, but it's more than just unpleasant. The Pentagon worries that jet lag will impair pilots' performance and endanger soldiers on missions, and companies worry that jet-lagged executives may not bring their "A" game to meetings and make bad deals as a result [source: Eastman and Burgess]. Those worries are justified. According to a 2010 study by University of California researchers, the brains of hamsters subjected to chronic jet lag created new neurons at about half the rate of normal stay-at-home members of their species, and showed memory and learning deficits as a result [source: Sanders].

There's growing evidence that jet lag may even harm your health, particularly as you age. A 2006 University of Virginia study, for example, found that while younger mice were able to rebound from the effects of air travel, being subjected to the equivalent of a Washington-to-Paris flight each week increased the death rate among older rodents [source: Wilber]. Other research indicates that jet lag can aggravate menstrual discomfort and even contribute to the development of heart disease and diabetes by altering eating patterns [source: Eastman and Burgess].

So what's a weary traveler to do? Over the years, people have experimented with all sorts of remedies, from jogging to trying to fight off sleepiness with frequent doses of caffeine, to various herbal and food-supplement remedies. While the magic bullet that would totally eliminate jet lag remains elusive, health experts say there's a lot you can do to help your body adjust to travel between time zones and to feel your best, no matter where you land. But first, here's some information on what causes jet lag, and why it makes us so miserable.