Dear Doctor ...

Dear Doctor: Whenever I travel in cars, I get sick. Is there a remedy? 
Kalemere, Kiboga

Dear Kalemere: Motion sickness is a condition in which confusion between visually perceived movement and sense of movement in the semicircular canals (organ of balance) results in fatigue, dizziness, nausea and vomiting. This can occur whether one is traveling by road, sea, or air.

The brain senses movement by getting signals from the semicircular canals, ears, eyes, muscles and joints. When it gets signals that do not match, the brain has an area that can be used to resolve confusion between what one sees and balance and is also useful in inducing vomiting when it detects poisons.
When the semicircular canals in the inner ear transmit to the brain that it senses motion, but the eyes tell the brain that everything is still, the resulting confusion makes the brain believe there must have been intake of poison hence nausea and vomiting to help expel the poison.

Looking out of the window of a moving vehicle towards the horizon in the direction of travel will tell the brain that one sees the movement that the semicircular canals are detecting, hence stopping the symptoms.
A nap (but not reading a book), closing eyes, or watching TV in the car will resolve the conflict between the eyes and the organ of balance. A nap also helps prevent psychogenic effects like fear of the problem which worsens it.

Fresh cool air, avoiding a full stomach or alcohol before or during travel and avoiding foul odors can all help. Where one sits is also important. The front seat of a car, upper deck on a boat or wing seats in a plane may reduce motion sickness.

Traditional drugs for vomiting may not be of help. Turning corners, bumpy roads or rough sea travel can worsen motion sickness.

Though anyone can suffer from motion sickness regardless of their background, children two to 12 years as well as those anxious about travel and those susceptible to vomiting (such as those in early pregnancy) are most likely to get the problem.