Why does spinning make you feel sick?

Kat: I think this is all to do with the vestibular system, if that's the right word. I'm sure Chris will pick me up on this from Australia if I'm wrong.

Basically, inside your ears you have a system of interconnecting tubes that are all at right-angles to each other. In each plane: up down, left and right that are filled with fluid. They tell you which way is up and which way is left and right in your head so you know if you're standing up or lying down.

If you spin very fast the fluid in these canals will spin round. If you stop very suddenly, as in stopping an office chair, you stop but the fluid in your ears is still going. Your brain gets all confused. You think you're still spinning but your eyes are telling you that you're not spinning so it manifests as feeling very sick.

Ben: Isn't this why people feel sick in long car journeys at all?

Kat: Exactly, it's when you get an imbalance between what your ears are telling your brain and what your eyes are telling your brain. You get confused and that makes you feel nauseous.