"I can't remember the way I used to remember. And they all came one at a time and they just slipped away, thank you. It is like somebody is in charge of you and they are saying, 'Right, I added all these bits when you were a youth, now it is time to subtract.'
"I can't work my left hand on the banjo. It is as if I am being prepared for something. Some other adventure, which is over the hill. I have got all this stuff to lose first and then I will be the shadowy side of the hill, doing the next episode in the spirit world."
Billy says he has "cut back" on work and in the doco, he is shown asking for filming to halt as he is in immense pain, and later he begins shaking uncontrollably.
"The Parkinson's is strange because it is not going to go away. All my life I have got sick and I have got the flu and pneumonia various things and they all went away. This isn't going anywhere. It is going to get worse.
"It takes a certain calm to deal with, and I sometimes don't have it. I sometimes get angry with it, but that doesn't last long, I just collapse in laughter. The good things are there, the love we have for people is still there, and with a bit of luck the love they have for you is still there.
"And I am very lucky in as much as I made a bit of a mark and you think, 'Well I must have done something right.' And that keeps you company when you are older, is the fact that when you were creative, you created well, it accompanies you, it is a great companion.
"You can volunteer to take life seriously but it is gonna get you, they are going to win over you, it is harsh, but you can either break down and complain about how miserable your life is or have a go at it and survive. I think that is the basis of it all."
In that same spirit, he adds: "There is still time to go yet, there are still places to go, new friends to make, maybe new songs to write and sing and jokes to tell."