Already need a few days rest.

I have been practically back pain free for almost two months...until yesterday.  It started in the morning and I didn't really think much of it, the doctor said it would happen so that's what I thought I was dealing with.  It progressively got worse throughout the day but I still felt like I could go to boot camp, especially after my recent motivational boost within.  So I get to class, start doing what we do and the pain is just too much.  I end up leaving class about 15 minutes early and while I am driving home I remember a recently forgotten memory from yesterday morning of me, while walking around the car parked in the street, completely biting it on the icy pavement.  I mean ass up, flat on my back fall on the ice.  I can't seem to figure out how I blocked this from my memory yesterday other than the fact that it did not hurt at the time, at all.  So now I give it a few days rest and see how I feel, then get right back to it.

You can actually see dudes face bounce of the ground.  Why is seeing people fall so funny?