We have a large maple in our yard. It had about a 12 foot high piece of trunk that was dead and ready to split off. One day while mowing I yanked on it, just to see how rotten it was. It came free easily, and somehow I managed to push it off to my side as it fell. I did not know my girl dog was coming up right behind me, she caught the trunk right across the middle and it pinned her to the ground. She looked to be dead, somehow I was able to lift the piece off of her and move it to the side. I started hollering for the wife as she's a vet, but she didn't hear me.
I started trying to shake the her to see if she would respond, and she started to struggle and choke. I think she was knocked out and also had the wind knocked out of her. She staggered to her feet, and I was able to get her in the house walking with her by the collar. When she got in the house my wife examined her, and said as far as she could tell, she was just bruised up. She gave her a pain pill, and she eventually recovered 100%, except she won't go by that tree. When I went back out to finish mowing, I could not move that branch even by dragging it. I had to use the mower and a strap. Weird.
Edit: I was also trail running after work one day, and an old ash tree fell across the trail right where I had been about 30 seconds before. I'm sure it would have killed me.