Fallen being unable to get my feet out of the clips. Standing perfectly still.

When I first started using the clipless petals, I quickly got the knack of taking my feet in and out. Then I went for my first (well it was supposed to be) longish ride with them. I was with a friend who just got on a bike and I had gotten to the top of a little rise, waiting for her. I was almost perfectly still, until something happened (lost my balance, wind blew hard, who knows) and I found myself going shoulder first into the grass.

Since then I've gone down three more times, all while standing perfectly still.