I have the same problem (I don't have MS however). I park in the handicapped spot because when I walk in, sometimes I have trouble walking out..I never know. One time I walked into a mall and almost couldn't walk out...it was an effort of will to make it to my car. Scary. I will also start limping in the middle of walking..it may or may not go away. Living with an invisible disability that isn't 'invisible' to us is difficult.