I don't have MS, but I do have some sort of weird autoimmune disorder that affects my autonomic nervous system and my stamina (I also have Hashimoto's thyroiditis and had a positive ANA test). Anyway, I thought long and hard on it, and even though stress definitely can exacerbate my symptoms, I felt the stress of not doing what I wanted to do would be worse than the stress of law school.
If I pass out while engaging in the Socratic method, someone will just have to put me back in my chair. No big deal;-). I think that old show with the guy in the wheelchair - Ironside? - may have made law a place more open than many others to people with disabilities. So, in my quasi-educated opinion, go for it!