Nausea and vomiting associated with any form of transport is caused by the same combination of factors. The main problem is that the two senses we use to balance — the eyes and the balance mechanism in the inner ears — do not synchronise. On a ship, the deck appears to be level, but we sense motion; in an aircraft, the interior of the plane appears to be horizontal, but the aircraft may be climbing steeply. Reconciling these conflicting sensations from our eyes and balance mechanism helps to overcome motion sickness. In a ship, sitting on deck (ideally amidships) and watching the horizon will help. In an aircraft, a window seat from which we can see the earth below and a seat over the wings where there is least motion are helpful. In a car, sitting in the front seat or in the centre of the rear seat, from where the road can be easily seen, will assist.
Being overdressed, too warm, in a stuffy environment, eating too much, and drinking alcoholic drinks will aggravate motion sickness. You should be lightly dressed, slightly cold, have plenty of fresh air, eat small amounts of dry easily digestible food before and during the trip (no greasy chips or fatty sausages), and avoid alcohol. Fresh air is available by going on deck in a ship, opening a car window, and opening the air ducts wider on an aircraft (don't hesitate to ask a flight attendant for assistance).
If you still feel queasy, there are also a number of medications for the prevention or treatment of motion sickness. A wide range of antihistamines are available in tablet, mixture and injection forms to both prevent and treat motion sickness. Milder ones are available without prescription, while stronger ones will require a visit to the doctor. Sedatives are used in some severely affected patients.
In chronic cases of motion sickness, the problem may be psychological as well as physical, and desensitisation by a psychiatrist or psychologist may be appropriate.