wow, that's terrible. I was a competitive swimmer in my youth, and we did similar competitions from time to time (very rarely). I've never seen or even heard of a swimmer passing out underwater.
A more common drill we would do in practice were called "hypoxic" sets, where we would do one length of the pool breathing every 3 strokes, then the next every 5 strokes, then 7, 9 etc.. until you were going across the whole length (25 meters) without breathing. Not everyone could do it towards the longer distances without breathing, and the coaches would look out for "cheaters", but never once did anyone pass out. Maybe most swimmers, by way of the typical training and exertion in the pool, just don't develop a very good suppression of the "breath signal". I also never remember seeing anyone purposely hyperventilate so that they can stay under water longer.
A more common drill we would do in practice were called "hypoxic" sets, where we would do one length of the pool breathing every 3 strokes, then the next every 5 strokes, then 7, 9 etc.. until you were going across the whole length (25 meters) without breathing. Not everyone could do it towards the longer distances without breathing, and the coaches would look out for "cheaters", but never once did anyone pass out. Maybe most swimmers, by way of the typical training and exertion in the pool, just don't develop a very good suppression of the "breath signal". I also never remember seeing anyone purposely hyperventilate so that they can stay under water longer.