Perhaps jet lag is the culprit. Crossing time zones while you travel is just one of the causes. Some advance knowledge and preparation can result in a more enjoyable trip.

PRIMARY CAUSES OF JET LAG

* Crossing two or more time zones: This is worse on eastbound flights because you have to adjust to an earlier schedule.

* Lack of sleep before you travel.

* Physical exhaustion from doing too much too quickly just before you leave.

* Dehydration: Aircraft air is very dry. Drink plenty of water (not soda, coffee or tea). Some people take their own bottled water with them.

* Disruption of the body's normal wake/sleep schedule (circadian rhythm).

* Alcohol consumption: Alcohol contributes to dehydration. At altitude, affects of alcohol are magnified several times.

* Stale air: Aircraft air is not as oxygenated as outside air. It also contains odors and minute particles emanating from passengers, crew, luggage and the aircraft.

* Inactivity and lack of exercise.

* Climate change.

POSSIBLE SYMPTOMS OF JET LAG

* Slow reflexes - especially dangerous while driving

* Sluggish thought processes - resulting in poor decisions

* Sleep disturbances

* Poor appetite

* Headaches

* Sinus irritation

* Gastrointestinal upset caused by unfamiliar food and water

* Fatigue

* Anxiety

* Disorientation

* Irritability

* Swollen extremities (especially feet and lower legs)

* Sweating

COPING WITH JET LAG

* Acclimate yourself before you leave. If practical and possible, schedule your alarm clock and meals for the new time zone a day or two ahead of time.

* Don't leave all your packing until the last minute.

* Make sure you get a good night's sleep before your departure.

* Choose appropriate flights so that you can arrive well in advance for activities like business meetings. Aim for daytime flying (in both directions).

* Set your watch to the new time zone as soon as you board the plane.

* Stay on schedule with medications.

* Drink plenty of bottled (not local) water.

* Avoid salad or foods that may have been rinsed in local water. This will help to prevent diarrhea - which can contribute to dehydration.

* Get up and move around instead of sitting in your seat for long periods of time.

* Wear shoes a half size larger to accommodate swelling feet.

* Once you arrive, don't spend all day cooped up indoors. Get out in the sun and fresh air.

* Take a hot shower before going to bed. This helps to retune your body's circadian temperature rhythm. The drop in temperature after you get out of the shower will make you start to feel drowsy.

* Schedule appointments when you are most likely to be rested.

EVERYBODY IS DIFFERENT

* Recovery time, as a rule of thumb, takes about one day per time zone crossed.

* Some people are more adaptable than others and exhibit very few jet lag symptoms. Children almost always fare better than adults.

* The more 'laid back' you are about schedules and daily routines, the more likely you are to cope well with jet lag.

With a little advance planning, your next plane trip could be the best ever!