I was on holiday on the island of Symi and my daughter challenged me to an underwater swimming contest - who could swim out the furthest underwater. I was to go first and dove in and started swimming with long measured strokes, none of this rapid flailing through the water nonsense for me. Sadly as I was swimming I was pretty much following the seabed which is very deep there, and going both out and down at the same time. When I was getting to the point of running out of air I opened my eyes and it was pitch black.
I started making for the surface as fast as I could but there wasn't even a glimmer of light and I started to panic, violently thrashing for the surface. The pressure in my head was something I have never experienced before as it felt as if my eyes were literally going to pop out of my skull, but by now I could see some light. I burst through the surface and couldn't really make anything out clearly as I had flashing sensations in my eyes and was gulping down air like there was no tomorrow. i turned to look at the shore and saw my daughter wave and then dive in, which scared the living daylights out of me, but she sensibly swam close to the surface and I could watch her progress easily enough. One bit of stupidity when I swam a few degrees down from normal and nearly paid the ultimate price.
I shudder whenever I read about drowning swimmers and wonder how many of them did what I did but just went a tad deeper.