system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: if brain damage occurs after about 4 minutes without oxigen, how can the world record for apnea be almost 25 minutes?

I'm first year in med school but I'm afraid this is physiology, which is a subject I haven't started yet. Feel free to explain this like you would to a first year med student instead of a 5 year old if you want lol. This is probably a really stupid question, but I really don't get it.

What exactly is the difference between not breathing because unconscious (so brain damage after about 4 mins without O2) and apnea/free diving while conscious?

You're still not breathing but your tissues and brain are obviously still absorbing oxygen from your blood flow, gradually decreasing the O2 concentration. Without new oxigen intake, you should still run out of blood oxigen in a couple of minutes, and surely taking a deep breath before holding it isn't enough to make it another 20+ minutes? What's so different then from being unconscious, and why the two times are so widely different?
gpt
People train very hard to reduce their body oxygen consumption and at the same time increase their lung capacity and blood oxygen absorption. So while for a normal person brain damage occur after 2-4 minutes the worlds best free divers with all their training and preparation can stay under water in calm conditions for about 10 minutes.

When you talk about 20-25 minutes that is not unaided. In order to do this the divers prepare themselves by breathing pure oxygen to fully saturate their blood and lungs for hours before attempting the dive. And still it is possible that the world records have only been possible using a variety of drugs to help increase absorbed oxygen and decrease oxygen consumption.