I've had a couple, but the one that brought me closest happened like this:
Down in Miami, I lived on a lake when I was a kid. We were like fish and back in the day we were allowed to go swimming without adult supervision as early as about 7 or 8. I was probably about 9 or 10 at the time and a group of us were swimming at my buddy's house. We were playing this game with a plastic ring that would sink and we were taking turns hiding it from each other and then trying to find it in the murky water. My buddy had a floating dock in his back yard, the kind that was made from two huge chunks of styrofoam with a 2 x 4 platform/frame built around it. It was probably 12' x 12'. If two of us stood on one corner of the dock, it would go underwater and the opposite corner would come up out of the water. If a heavier person climbed up out of the water on to the dock, then the opposite side of the dock would raise up, no matter where the person was on the dock when climbing out of the water.
Anyway, when it was my turn to hide the ring, I had the bright idea of putting it under the dock. As I was swimming under the dock, a bigger teenager that was swimming with us started to exit the water by climbing up in the middle of the dock. I was already underneath about right in the middle and when the dock leaned up from the teenager's weight, I saw daylight. I assumed that it would take him longer to climb up on the dock, so I attempted to exit the water by continuing forward toward the shore. Right at that moment, the teenager jumped off the dock and the dock came crashing down on me, pinning me to the coral bluegill beds. I struggled for about thirty seconds, my life flashing before me. Unable to move or scream, the desperation, helplessness, fear, and every other scary emotion that you can come up with coursed through my entire body. I thought I was a goner.
Just when I was about to give up, the dock magically lifted up and I was able to scramble to the shore. Out of breath with my chest all scratched up, I laid on the shore on my belly while my friends continued frolicking, oblivious to what had just happened. I turned and looked and the teenager that had jumped off and caused the dock to pin me was standing on the corner of the dock, with the opposite corner way up high in the air. He, too, had no idea what he had just done. He almost caused my death. By chance, he decided to get back out of the water in time for my life to be saved. My friends, being young and oblivious, would have never even noticed I was missing until it would have been way too late. I guess it wasn't my time.