Physiological & biochemical processes of the body get adjusted to a 24-hour periodicity of daylight and darkness and follow a rhythm which is generally known as body clock. When a person travels across a number of time zones in a short period of time, the body processes cannot get synchronized with the daylight-darkness periodicity of the destination and the body processes get disoriented. This condition is generally known as jetlag.

Persons traveling long distances by jet aircrafts commonly face this condition and hence the name jetlag. For some people their working conditions create an environment which has a different rhythm of body activities effectively creating a different daylight-darkness cycle. Persons who work in night shifts for long periods or work for long hours at a stretch for a number of days are common victims of this condition and suffer jetlag.

Loss of appetite, mild depression, loss of inability to concentrate, irritability, being confused or forgetful are common symptoms of being jet lagged. The affected persons may also suffer from swollen or uncomfortable feet, dehydration, disturbed sleep pattern, etc.

In case of travelers it is the time zones crossed and not the length of the flight-time that matters. For instance Frankfurt to Johannesburg journey would not cause jetlag since they lie along the same meridian (and hence same time zone); it may cause tiredness due to length of time spent sitting up or headache due to low cabin pressure for a longtime but no jet lag.

On the other hand a journey between New York and Los Angeles may cause jetlag. Near north and south poles, where depending on the time of year, there are extreme periods of daylight or darkness; jetlag effects can be quite severe in these areas.

You can take a few precautions to avoid being severely jet lagged. A good night's sleep prior to a journey, having light meals and drinking plenty of non-alcoholic fluid in the aircraft helps in reducing the jetlag effects. Remove your shoes and stretch your legs to avoid swelling of the feet. Take some exercise like walking up and down the aisle, stretching, etc. to avoid discomfort.

Melatonin, some people believe, is a drug that can help in avoiding the jetlag; it is required to be taken for a few days starting with a couple of days before the journey and continuing for a few days after it. It is required to be taken at specific times. Research has shown that its claim cannot really be supported and on the contrary, in some cases, it may lead to worsening the effect of jetlag. In UK it is banned.

Anti-jetlag diets are available on the market. But it is a cumbersome process to follow the diet for a number of days; it is not very practical solution. It is a mistaken belief that sleeping pills help you get over the jetlag; you are strongly advised against it as it can cause other complications. A homeopathic drug, "No Jet Lag", is said to be effective and being homeopathic medicine it is stated to be free of side effects.