I don't find MS scary. From what I've read it's not lethal, nor lifespan shortening, and it's easy to take care of. I think the fear comes because many symptoms of anxiety mimic it, and other diseases.
You hear a lot about brain tumors and hypochondriacs. We're not just scared because our brain is our most precious organ, we're scared because of symptoms. When you have dizzy spells, tension headaches that won't go away, or vision trouble you don't think "Oh, well, that's just intense stress". You think your brain is damaged, there's something in your brain or on your brain. You research and find symptoms for tumors, like headaches and dizziness, and panic because that sounds like you.
I remember fearing MS once. I actually took comfort in telling myself I probably have Multiple Sclerosis or fibromyalgia; it was better than the other things that worried me. That random pain? Just my fibro, don't worry. That cold ice feeling under my skin? Fibromyalgia, obviously, don't panic.