I'm a paramedic.
Last night, on duty, we were called to a local gym and indoor pool facility for a teenager found drowned in the pool.
He was alone. Nobody knew how long he'd been under. Some gym goers walking by noticed he was just floating under the water and grabbed him out.
They did CPR, and thankfully, by the time I got there, he was wide awake but in a lot of pain.
He admitted to me later that he was trying to swim long lengths underwater and his last memory was trying to come up for air and then nothing.
He experienced a shallow water blackout. Essentially, when you are trying to do long distances underwater, you can hyperventilate to maximize your oxygen intake and blow off much of your CO2, thus reducing the feeling of 'i need to surface for air' during your laps.
But what ends up happening sometimes, is that you overdo it, and you end up expelling too much CO2. Then, as you are doing your lap, your brain becomes oxygen deprived, but the CO2 level in your body is too low for your brain to signal you to breath.
And, without any warning, lights go out. No slow fade into darkness, no slow feeling of passing out. No, you pretty much just go out in a matter of seconds.
...
At the hospital, my patient's father expressed shock to me that this happened to his kid. His kid is an incredible competitive swimmer, one of the best in his age group. It didn't make sense that he nearly drowned. He could understand some rookie, but his kid? In a pool that was maybe 5 feet deep?
I told him yes, his kid, in a shallow pool, surrounded by other people. He almost lost his life before he even started it in earnest.
Don't. Train. Underwaters. Alone.
