Neurological explanations
Epilepsy
Your brain cells send electrical signals to your body to tell you to do things, like move. Normally, the brain fires electrical signals in a controlled way. In epilepsy, the brain fires electrical signals in a random and uncontrolled way. When a fit happens, the brain cells are a bit like people at a rock concert. One person starts screaming and dancing, then those nearby do so too. And before you know it, it spreads all over and everyone is dancing and screaming chaotically.
We can give medication to try to stop electrical signals from firing randomly.