Being trapped inside your mind with no control over your body would be terrifying, and, unfortunately, it does happen to some people. It's something called "locked-in syndrome" and is very often confused with a true vegetative state.
The main difference between locked-in syndrome and a vegetative state is that people in a vegetative state have no brain activity. Patients that suffer from locked-in syndrome have fully functioning brains and are aware of their surroundings, but they're literally locked inside their own body and unable to communicate. Until now.
Scientists have discovered a way to tell the difference between patients in a vegetative state and those with locked-in syndrome, and even a way for them to communicate to their loved ones.