Parkinson's must have been terrifying. To someone who relies so much on physicality, someone with so much energy, it must have seemed more daunting than death.
His outbursts were a way of controlling or perhaps overcoming the fear and anxiety inside him. As long as his body listened, he could stay one step ahead. Once it stops obeying him...

I hurt for him and his family. His poor wife. I hope she has a support system.