The revered comedian was diagnosed with the degenerative neurological condition in 2013 and will appear in the second part of his BBC documentary series Made In Scotland on Friday.
Sir Billy will reflect on his life and career in showbiz while insisting he is not scared of death.
According to the Daily Mirror, he will say: "My life, it's slipping away and I can feel it and I should. I'm 75, I'm near the end. I'm a damn sight nearer the end than I am the beginning. But it doesn't frighten me, it's an adventure and it is quite interesting to see myself slipping away.
"As bits slip off and leave me, talents leave and attributes leave. I don't have the balance I used to have, I don't have the energy I used to have. I can't hear the way I used to hear, I can't see as good as I used to. 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'."
Glasgow-born Sir Billy, nicknamed The Big Yin, was a welder in his home city before becoming a globally-renowned comedian.
He was diagnosed with Parkinson's - a neurological condition that impacts movement and speech - while undergoing surgery for early-stage prostate cancer in 2013.
Sir Billy has turned 76 since the BBC documentary was filmed and has had to cut back on performing due to his illness.
He is known for his energetic performing style but said Parkinson's prevented him from moving around the stage like he did at his peak.
At one point during the programme, Sir Billy, who is married to psychologist Pamela Stephenson, reportedly asks for filming to stop as he appears to be struggling with the effects of the disease.
Speaking about Parkinson's, he said: "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."
Billy Connolly: Made In Scotland will air on BBC2 at 9pm on Friday.