Traveling long-haul crossing different time zones causes jet lag. This is because the body's internal clock is yet to be synchronized with the external clock in the new time zone. Some of the symptoms of jet lag include insomnia, sleepiness, impaired performance and diminished alertness. You can be easily irritable, or be in a depressed mood. Apparently, jet lag can also result in gastrointestinal distress.
A general rule of thumb to keep in mind before any long trip is the 1:1 ratio: allow yourself one day to recover for every hour of time difference that you experience.However, I personally find this to be rather extreme as I will lose my vacation by the time I've recovered from the jet lag.
You can try to reduce the effects of jet lag by setting your watch to the destination's time as soon as you get on the plane. This way, you can sleep and eat accordingly, adjusting your body to the time in the destination's time zone.
