Jody:
You ruptured your plantaris. I did this exact same thing over a year ago, then did it again and again in a series about six months ago. It is a very small, pencil-like muscle that is evolving out of our bodies, but hasn't quite completed leaving the building.
Actually, I believe this is the same injury (the first one) that sidelined Cathe from filming the new videos.
I just did SPC last week, and it was the first step workout I have done for four months. And I didn't pop the plantaris, so am hoping that it finally healed enough to slowly start doing step again. Look it up on the internet and you will see that it happens as you are stepping back and down off of a surface (step, in our case).