Roger
The evidence for benefits on REM sleep in Parkinson's seems to be based on a single non-blinded case series of 4 patients. I am sure that all the doctors on here would agree that that is interesting but not evidence.
I no nothing about the possibility of harmful effects of CBD on people so cannot comment. The Parkinson's foundation or davisphinney might be worth looking at as well as discussing locally with your Parkinson's nurse, therapist, doctor.