Jet lag is a normal consequence of traveling rapidly across several time zones. It occurs only when flying east or west, not north or south. Jet lag can be a relatively minor problem, resulting in fatigue, reduced alertness or mild disorientation, or it can be a major problem, as when it becomes impossible to stay awake on the job or behind the wheel of a car.
Fortunately there is a safe, natural way to combat jet lag. Exposure to intense light at the appropriate times and avoidance of bright light at other times can rapidly reset the internal biological clock that controls the sleep/wake cycle. A lightbox can be used when intense light is needed and natural sunlight is unavailable. Some lightboxes are sufficiently portable for travel, and some hotels - particularly in Japan - provide lightboxes for their clientele. To avoid exposure to daylight when this is undesirable one needs only a blindfold for sleeping and good quality dark glasses to wear during waking hours.
Other than staying on your home schedule while away – which is rarely possible for trips of more than three days' duration – the way to avoid jet lag is to shift ("phase shift") ones internal biological clock as rapidly as possible into the time zone of your destination. When traveling east you need to "phase advance," and on a westbound trip you need to "phase delay." The exact timing of light-exposure and light-avoidance varies with the number of time zones traversed and with the direction of travel (east or west.) The effort required to phase shift is well worth it. You will be able, for example, to travel halfway around the world - through twelve time zones - and synchronize your internal clock to local time in just three days, rather than suffer disorientation and discomfort for two weeks or more.
People who work irregular shifts often develop a variant of jet lag without ever leaving home. They may have trouble adjusting to a new shift and become sleepy or "spacey" at work. This may be merely inconvenient for some people, but it is a serious matter for health professionals, those involved with public safety or people at risk of injury on the job. When "human error" has been identified as a cause of a major disaster, such as the explosion at Three Mile Island or the Challenger Shuttle, it is very likely that shift-work schedules played a role. Because most of the world operates on a daytime schedule it is difficult even for regular night-shift workers to avoid sleep deprivation at times, particularly if their schedules are markedly different on days off than on working days. One reason that night workers are at high risk occupational accidents is that humans are biologically programmed to be less alert late at night, when our body temperature is lowest.
There is a safe and natural way to reduce some of the adjustment problems of shift-workers. Exposure to intense light at the appropriate time can improve alertness and reset the biological clock that controls the sleep/wake cycle. While this can sometimes be achieved by going outdoors into the bright sunshine at certain times (and by using a blindfold to block out light when sleeping), a lightbox is the most effective way to provide sufficient light for this purpose when intense natural sunlight is not available.