I once fell form my bike and fell chin first into the concrete when i was 11. I didn't notice I was bleeding until a worried lady told me. Also she happened to work at a clinic or something so she had bandageds and stuff and drove us to a hospital in her van. I had to get stretches under my chin. During the whole thing I didn't feel any pain, also because the doctors numbed my chin before giving me stitches. So basically what I'm getting at is that it's pretty cool how the body sometimes makes us not feel pain as a way to protect us.
