I lucked out on having a PT guy who understood MS. I was one of the few allowed to bring a water bottle on the floor in case I overheated from exercise. He was still a drill sargent when it came to the exercises , but he also understood that there were limits to what I could do. We started with simple balance exercises before they had me increase slowly. One strength exercise I tried a couple of times, but they realized I couldn't do it unless I was sitting down, and they accomadated me.

When I started out in the pool, which was very warm - they knew they had to help me out of it. Both for the bum knee and because of overheating and muscle fatigue. Ask for a consult with him the next time you go in. A good PT guy will take the time to figure out what's going on without judging you.