Feeling dizzy and like you want to throw up because you are in a moving vehicle - that is called motion sickness.

The fancy name for it is kinetosis, though the more common ones are seasickness (if you are on a boat), carsickness (in a bus or car) and airsickness (a plane). Many astronauts experience spacesickness too.

It happens because your body has different ways of knowing if it is moving - and sometimes, one clashes with another.

The most obvious way we tell we are moving, and in what direction, is by looking. Our eyes pick up changes in light and shapes, and send that information to the brain.

Then there are the ears. In your inner ear is a tube called the cochlea. It is filled with liquid, which tells your brain if your body's position has changed.

Imagine a water bottle on a car seat. If the car drives down a slope, the liquid sloshes to one side. And if the car goes up a slope, the liquid sloshes to another side.

The cochlea is lined with nerves that send signals to the brain, so it picks up changes in your position and movement - even if your eyes are closed.

Your skin and muscles also send the brain updates about your movements.

The brain takes these bits of information and puts them together like pieces of a jigsaw puzzle, to figure out what your position and movements are.

But sometimes the pieces do not fit. If you are on a boat at sea, but in a compartment with no windows, the inner ear says you are moving, but the eyes say you are not.

When this happens, your body responds by feeling sick. Why? Many scientists think it is because your brain always believes your inner ear over your eyes. If they disagree, it figures your eyes must be imagining things because you are sick or have eaten something poisonous. And the best way to get rid of those poisons? By forcing you to empty your stomach!

How to prevent motion sickness

People usually feel motion sick when they are having a bumpy ride of some sort. You can also get it while sitting in a vehicle facing backwards or while reading, or being in a boat cabin with no windows.

Experts usually advise you to sit facing the direction you are travelling in, and to look at the horizon or objects far away so your eyes get all the right information.

You should also try to sit in a part of the vehicle, boat or plane that does not move so much. There are also medicines that can stop you feeling sick.

Photo: AP