Once when I was little, round 6 or 7, I jumped off a diving board and didn't realise how deep the pool actually was (think it was about 5 meters) so I thought I was going to drown because it felt like forever until I reached the surface, a lifeguard had to pull me out with a stick and I had a fear of diving for years.

Luckily, i'm way over that fear now and love diving boards.