Nothing serious for me. I went on an inflatable balloon sort of fun tunnel during a festival, and there were two passageways. I was on one side and a girl was on the other. My Dad was goeding me to beat her to the end, and once I got to the end, the girl bounced on her side causing my side of the tunnel to rise up and send my 7 year old body flying. I landed on my head, and almost cracked my skull open. I was unconscious until I found myself in an ambulence to the hospital, and I suffered no damage to my head.
What's ironic is that I probably hit myself on the same spot of my head that same year when I crashed into my sister's bicycle also sending me flying. Maybe that explains the bump I still have on top of my head.