Wow man, that’s bad. Bad in a sense that I hope it does not take away you being able to play an instrument!
It’s funny I am a lefty and play with right handed like you do - do that with almost everything. It is not funny that I have herniated C4-C5 and am somewhat in the same boat as you, however I can get mine fixed at some point. When diagnosed (my neck locked up on me and put my chin on my shoulder) I was told it was pre-existing and I had hurt it in the past, told me I was a freak of nature as the way it was herniated that I really should not be able to use my left hand/arm (herniation pinched the nerves). Doc told me I was much to young to have the operation and since i was not in pain that I should wait until the day comes when I wake up and lose the use of my arm or hand and then I could have the surgery done. He did tell me that it could and would happen “any day” (and that was 8 yeas ago) and he told me to not be alarmed as I would eventually wake up one day and not be able to move my arm/hand.
As far as my playing: Well my damn left hand simply falls asleep a lot when I use it. It is really common for me to have to shake my hand for the 1st hour of playing as that dude “falls asleep” and is hard to get the tingling out…but if I keep shaking it and shaking in between songs/practice it will cooperate and get going after and hour or so.
Now to inject some humor but to not take away form the seriousness of your post/diagnosis - Man doesn’t it suck getting old and falling apart? I am in great shape for my age (42) but with heart, neck/spine, gurd, and vision problems starting to show up I can only say that it is down the hill all the way to the bottom from here!
Wish you the best of luck man, modern medicine is amazing and I hope you can find something to either cure/overcome the Dystonia.
A question though as I know little about it - Does it only effect one extremity vs both (in the case of your arm/hand)?