Just a clarification on that first incident about the U.S. Navy Seal hopeful. He drowned because of holding himself underwater for several minutes at a time without a "buddy", not a swimming drill with his off-duty lifeguard friend. That doesn't at all preclude blackouts from happening during supervised swimming drills, but that particular example is not a swimming activity, just a water activity.

As far as I know, his death was a result of doing a dangerous activity alone during an otherwise busy open lap swim, combined with the fact that he was not immediate recognized as a victim because he did his breath-holding thing in the extreme corner of the pool, and some possible inattentional blindness as a result of weeks of asserting to the lifeguards that he knew what he was doing. That last point has been the more interesting topic of discussion to me. The guard didn't see the drowning because it looked exactly like what he'd been doing for weeks, and it was completely silent. How this was allowed to continue? Given what I've seen, it was one of/a combination of the following:

• the lifeguards trusted him when he said he knew what he was doing
• deferred to other lifeguards that had allowed it (precedent argument- longer it goes, the harder it is to stop)
• deferred to the "off-duty lifeguard" buddy, then continued to allow the victim to hold his breath based on familiarity
• simply didn't feel confident enough to say 'no'/concluded that it wasn't worth the argument
• or didn't get any clarification from the supervisor/facility about a grey area in the rules

The result was that on the day he pushed himself too far, he had already been underwater for several minutes in a extreme corner of the pool. Because his friend was not there spotting him, no one noticed until it was too late.

Anyway, relax. What that guy did was dumb and motivated by some fitness test for a Navy Seal thing. It doesn't pass the common sense test, and it's not the same thing as lowing your breath count during supervised practice.