Irrational Fear Meme

Rebekah has started an Irrational Fear meme. I knew immediately what I should post, because I have one huge, stupid, irrational fear.

I cannot start down a flight of stairs without envisioning my ankle giving way, causing me to tumble all the way down. Obviously, I really like holding on to the rail when I go down steps (or at least for the first few steps).

I understand a bit about this fear -- when I was younger, I sprained my ankles all the time. I also had a habit of stepping off of curbs and falling down. But I've never fallen down a whole flight. Oddly enough, my sister did once (with a giant suitcase falling with her), but my fear pre-dates that.

So -- what's your irrational fear?