My first job in the sleep field was working in the Neurosciences Division of the Royal Air Force Institute of Aviation Medicine (IAM). At the time (the early 1980s) the IAM had one of the best sleep laboratories in Europe and much of its research looked into jet-lag and shiftwork.
Jet-lag occurs because your body clock is unable to cope with the lengthening or shortening of the day that is involved when we travel across multiple time zones: our body rhythms become out of sync with local time. As a result, you may feel fully awake at odd hours, or very sleepy during important meetings. Your appetite may be affected and your mental and physical performance reduced.
Almost all travellers will suffer some of the effects of jet-lag. Unfortunately, the only real way of completely avoiding its effects is to go by sea, as it gives your body time to adapt to the changes in time-zone! As a rough rule of thumb, it will take about 1 day to recover for each time zone you cross: for example, it can take up to a week to get back to normal after a flight from New York to London.
The following advice may help reduce the effects of jet-lag.