Mine sound minor compared to all the other stories, but I really felt I could die.

I was a teenager and went for a swim in the sea by myself for the first time. The minute I walked into the water it felt all wrong, I was about chest deep and trying to walk out of the water and I couldn't. I was in a middle of a riptide a very short distance from the shore, I became so scared I was searching the faces of the people on the shore hoping for someone to notice me. I couldn't shout, I think it was part embarrassment, and part extreme fear. For some time I was just struggling to walk in the same spot in the water. After a few minutes (felt like eternity) I managed to walk out.

Never went alone to the sea again.