When dopamine levels fall movements become slow and awkward.
It is a progressive condition which has no cure, but can be treated and can often take many years to develop.
About 18 months ago, when he realised he was experiencing trouble with his left foot, he had an idea.
"I didn't know how long I would have left to ride - so while I was riding along that day I made a decision." The decision was to ride 22,500km around Australia.
But more than that, he decided to use it to raise funds and awareness and dubbed the 97-day journey, which he set out on in February last year, as the "Ride For Parkinson's".
He used one of his four Italian Ducati motorcycles for the venture.
"I've always loved Ducatis and I've got four of them," he said.
He had hoped to raise about $15,000 but at the end of the ride had drawn in $34,000.
Since that ride he has decided to sell his property, at Stone Hut, just out of Adelaide, and move back to New Zealand.
"There are only 23 people in Stone Hut and they all know who the noisy one is."
He also made another decision - to do a similar fund and awareness-raising ride around the country he was born in and returning to.
So he made a few calls, made a few contacts and put together a schedule in what he hopes will raise about $5000, as well as awareness.
When Grant Woolford at Cyclespot in Takapuna heard about his plans he immediately offered to provide a motorcycle for Mr Stockwell, to save him the expense of bringing one of his over.
It is (of course) a Ducati Hypermotard 821.
"They were so good - everyone has been so good."
He set out from Auckland on February 27 and on Monday arrived in the Bay, having already called at Hamilton, New Plymouth, Taupo, Tauranga and Whakatane.
He was special guest at a luncheon put on by Parkinson's Hawke's Bay.
"It was a great day," he said.
He tells people during his meetings with Parkinson's societies, along the way, that he was never afraid.
"I never went into a black hole and accepted that okay, I've got Parkinson's but hey, I could have something worse ... you just have to get on with your life."
Meeting so many people, who had similar determinations, had been humbling, Mr Stockwell said.
"I talk openly about what I've got and how I just have to get on with life - I just hope I can pass on some hope and inspiration along the way."
He said his level of Parkinson's, which he takes daily medication for, did not affect his ability to ride a motorcycle as it had no effects on his balance or ability to operate the controls.
"I tell people I'm a medical condition with a motorcycle problem," he said, adding he was enjoying "getting used to the corners again" after years of riding the straight outback roads of Australia.
He headed south yesterday for Wellington and the South Island.
"I've started thinking it would be nice to do America - Parkinson's is also a big issue over there," he said. "It'll take a bit of work, but it's on my mind."
