Once. I was 18 years old and canoeing down a river with friends. Somehow, we hit a log pile with some speed and I was thrown out of the canoe and swept underwater. I found myself pinned against underwater logs and trapped by a strong current.

When I tried to move, I realized my foot was caught. Nothing I did would free it, and at that moment I realized that the end of my life had come and that I was going to drown to death.

I remember being absolutely terrified as I struggled and then reaching a moment of utter calm when I realized there was nothing more I could do.

When my body relaxed, the current itself freed my foot from the log pile, and I popped to the surface and breathed.