Sugarpud, the hardest thing about meditation is switching off the conscious mind.
If you have PD, that makes getting into a consciously thoughtless state even more difficult,
especially if you're on something like Ropinirole, which then makes it even harder.
Please try telling yourself that you can switch off thinking any time you want.
It's a good way to start.
I still have real problems switching my mind off, so you're not alone :)
Walking is good, though :)
My Tai teacher always said: If you can walk - you can do Tai-Chi.
Tai-Chi apparently stopped Chen Man Ching's TB symptoms.
Perhaps it might do the same for PD sufferers.
The downside is that you wouldn't get much appreciable benefit, if any,
Also, you would need to practice it every day.
When I did it, my posture got a lot better, and I became a lot calmer and more confident.
(I don't have PD, but I am a carer for my friend.)