I completely understand the feelings of impending doom. All I can say is that most of the things I really feared happening never actually did. It was very black and white to me, very all or nothing, very extreme. I didn't fear that maybe my arms or legs would get worse...I would think the same as you and go all the way to the ending thinking "Maybe I will COMPLETELY lose control of my limbs." You're putting an incredible fear into your mind when you do this...and believe it or not that itself will take a toll on your body.
PLEASE try not to worry about
the most terrible things happening, and just deal with things as they DO happen. They will happen whether you worry about
them or not. But remember that worrying can exacerbate things simply by stressing out your mind and body.