Alzheimer's
Burned alive...
Slowly and painfully, knowing that you're going to die.
Alone.
Being eaten alive by an animal.
Being burned alive.
Being murdered or choking on your own blood.
Getting your head chopped off.
By sex craved aliens from outer space
Someone killing you like a murder.
By some disease that destroys your body, but your mid stays sharp. Can you imagine having a mind that is functioning but you can't get your body to communicate that?