My Dad lived with it for 15+ yrs (his pic is my avatar). He passed in 2012 indirectly from Parkinsons (I'll explain). He lived 1400 miles away, so I don't know specifics of what his treatment was, or what he took, I can only share what I saw/heard on my visits up to see him.
My Dad had always been a self employed plumber/contractor, and he was able to continue with that (on a smaller scale) probably for close to 12 yrs. For my Dad, it didn't get really bad until the last 4 yrs or so.
I don't know the medicine he was taking, but it was specifically to help control the shaking. Problem was that if he took too much, he went off to left field, acted like he had dementia or something. He wouldn't know where he was and would talk about things that had no correlation to what was actually going on. I had no idea about this until one of the last 'pleasure' trips to see him. We decided to go somewhere to eat out. Being self conscious about his shaking, he took more of the medicine before we left. By the time we left the restaurant, he was talking about how he was glad to be done with that job, and at one point, tried to get out of the car at 70MPH thinking we were at his next job.
Proper dosage, or no medicine, he didn't exhibit any of this.
The reason I say the Parkinsons got him 'indirectly' is because his work was his social outlet. When he could no longer work at all, his world suddenly got real small and I think it got to him (he lived alone, his wife had passed in 2000). While I can't say I'm 100% sure it was a suicide attempt, it sure looked like it. He passed a few months later. He was 71.
What was crazy with my Dad was that he smoked pretty much his whole life, and drank quite a bit for awhile there, but Parkinsons was they ONLY thing wrong with him.
From what I read back then, Parkinson is not hereditary, but can possibly be caused by certain toxins in the environment. I had read somewhere that lead exposure may be a cause. Well, he was a plumber, and worked with lead numerous times. Connection? I don't know, but it made me wonder.
As for drag racing, how far along are you with the Parkinson? You may be able to continue for awhile. My Dad never gave up driving, but that's not piloting a car at high speeds. Maybe you need to look at it in terms of being more like a crew chief? Or maybe take up demo derby instead?
Stay active, surround yourself with family and friends.