I can't read the posts above, just as I can't watch any of those emergency programs where people get injured. It really frightens me and I prefer not to see or think about what could happen, but I do take great care when using machinery.
My most frightening experience was whilst building my extension. I was nailing the joists with a 4" nailer. I was working at arms length and nailing two joists together, I hit a nail plate and instead of the nail going into the wood it bounced back and hit me on the forehead! I pretty much knew that it wouldn't have the energy on rebound to penetrated my head, but I wouldn't dare feel to see. I had heard of head injuries where people felt no pain despite having things stuck in their skull. I scurried around the floor trying to find the rogue nail and sure enough I did, It had been formed into an almost perfect circle. On examination, I just had a small graze. I still have it somewhere as a reminder.
A week later, I was at A&E after breaking a finger cycling and started a conversation with a guy beside me. "What happened to you" I asked? he held up his hand and there was a 2 inch nail right through his finger. lol!! faint!