Ooh, Karen, that is scary! I'm glad you didn't lose control and wipe out! But I'm glad you may have found the cause of the problem. I'm glad I read this so that it doesn't (hopefully!) happen to me anytime soon.
There was that little panic moment when I wondered if the end result would be just that, but then I remembered, quit TRYING to pedal! Clip out, stop, and deal...
Sure was a waste of perfectly good momentum getting up that next hill, though!