I had PT for my knee. Damaged it big time falling off a motorcycle I was learning to operate.

I told them upfront that I had MS. I told them from the get-go that if I feel that I'm pushing too hard, I will have to stop. After the first few sessions of letting them know where my limits were (also known as putting my foot down), they accomedated my need to go easier than most of their PT patients. They also made sure I always I had something to grab onto if I needed it.

Also ask them for any home exercises you might be able to do on your good days. It helped me a lot.

Best of luck!