What did you do?

I've thought about this a lot question a lot, wondering over and over how best to respond.  It might seem like a simple enough question on the surface.  But trying to find a way to respond that is best for me and the person questioning can be difficult. 

Let me start at the beginning for you, where this begins anyway.  Muscular Dystrophy, myotonic dystrophy to be specific.  It is important for me to state that I am not at all embarrased by my disease nor am I in any way ashamed, nor do I feel like I have a particular burden in life to carry.  It simply is what it is.  "Myotonia is a symptom of a small handful of certain neuromuscular disorders characterized by the slow relaxation of the muscles after voluntary contraction or electrical stimulation. Generally, repeated effort is needed to relax the muscles, and the condition improves after the muscles have warmed-up." So, for me this often results in a fairly significant limp or staggering gait, until my muscles have warmed-up or been able to relax.  I can't control it and I don't know when it is going to happen, it is nothing that I can feel in advance.  So it is very noticible.  I have been known to stumble occasionally, although rarely fall.  Sometimes I have no limp at all, sometimes I limp a lot.  So, the question(s) often comes up: "What did you do?" "Did you hurt yourself?" "Are you okay?" or the dreaded comment about my age!  So how do I respond?  How would you? 

I have tried to defer with the 'I'm fine' or waving away the question with a smile and a wink, like I have a sceret or was caught in the act or something.  But more often than not especially at work, the questions persist.  'Really, can I help you? Should you be doing that' and on, and on.  Because I know the questions come mostly from a place of concern I am not bothered by them, it is not that people are nosey but concerned.  And so I answer as best and as simply as I can.  I say that nothing is wrong that I have MD and my muscles are a little stiff but that they'd loosen up in time and I'd be fine.  But then, more often than not it happens, the person in question mumbles something about not knowing, averts their eyes and tries to make a quick escape.  I have embarrased them, leaving them to feel as though they have opened a door best left unopened.  My intent of course is not to make anyone uncomfortable meerly to answer their question.  I don't want to lie and say that I hurt myself or something of the like as that just doesn't seem right.  I am direct and choose to answer that way yet I don't wish to make anyone feel badly.  I don't tell the truth to engender sympathy because I don't  need sympathy.  I am living well it just happens to be with Muscular Dystrophy.  I have been extraordinarily Blessed in my life and have nothing to feel sorry for myself for. I work hard at being a good steward of God's love, a hard worker, and the best that I can be.  Sometimes it is difficult to live with the pain I wont lie, but I really don't think that I have ever thought of myself as having been cursed or saddled with this disease nor have wished that it was someone else instead of me.  It is me and I don't mind talking about it.  I try not to bore people with the details, but if you ask I might tell you. So, why does it make people so uncomfortable?  Is there a better way to answer that question?  What would you do?  If you were to ask me that question, how would you like for me to answer you? 
I'd really like to hear from you.