Inside your ear is a little pool of liquid which does two jobs. First of all it helps (along with tiny ear bones) translate sound into signals your brain can process. Secondly, it helps with our balance. It’s like a spirit level you might used when putting up a shelf – a bit of liquid sloshing about can tell you if something’s flat.
When you spin round and round a lot, the ear-liquid turns too. You can then stop suddenly, but the liquid carries on for a bit! Like when you stir some tea: you may stop the spoon after a while, but the tea keeps rotating for a few seconds. Since your brain needs this liquid to tell when it’s balanced, if the liquid is still whizzing round, your brain thinks the world is spinning round, too! That’s what dizziness is 🙂