I find the shocked looks on nosey people's faces when I say "I don't want to talk about it" to such questions remarkably satisfying!
I no longer drive - as you don't know me, I'll tell you why. Many years ago I was rigt behind a horrendous Mway accident and was unable to save a small child in the back of one of the cars. I don't want to explain this at the school gates as you can imagine so I always say, "I don't want to talk about it". People quickly change the subject.
If you want to wind them up you could always tell them an outrageous, patently ridiculous story.... "Well, it was ever since my secret lover caught his willy in the door of my husband's Saab and had to be airlifted....!". People generally realise that you're taking the pee out of them and ease off on the questions.
I'd agree with TAFkA though, whatever you say, don't lie about an illness you don't have or you might never hear the end of it.