Oh heck yeah, let's do it! I also want to take it like this when I'm on the receiving end but similarly have a touchy gag reflex. Maybe we can help each other work up to it hehe... 😇

And in the video, they're in a sealed chamber with decreased atmospheric pressure, which decreases the partial pressure of oxygen. Even though the air still has 21% oxygen, it can't "push" itself onto hemoglobin as well, so it's an identical effect to decreased oxygen in your lungs.

This table shows this transition for altitude (which can be directly converted to oxygen saturation using a basic formula).

en.wikipedia.org/wiki/Time_of...

Oxygen isn't an all-or-nothing thing. When you put the cap on, you're using the oxygen held in your lungs at a somewhat steady rate. As the amount decreases continuously over the next seconds to minutes, you slowly transition from fine, to impairment, passing out, and eventually dying.

You may find this article and related topics useful: rackwiki.org/wiki/Breath_.... Feel free to DM me if you want to talk about anything in more detail, and I hope you stay safe!

If you're going to take risks, please don't overestimate your understanding of them. If there's anything that I've learned in the past few years, it's not beginners that usually die, it's folks who have quite a lot of experience but are missing a key detail in a circumstance they don't anticipate.

Your life is literally depending on it always being true that your CO2 levels will rise high enough fast enough that the burn will become unbearable before your oxygen falls too low. This may not always happen. Whatever you do, DO. NOT. EVER. hyperventilate yourself before you put the cap on.

Thus, you don't need to fully pass out to die, you just need your oxygen level to fall low enough that you're too confused to take it off. Once you cross that imperceptible line (even if you're still conscious and air hunger starts to kick in), you may be helpless to save yourself.

Please watch this video of trained military pilots trying to figure out how/when they are hypoxic: www.youtube.com/watch?v=UN3W...
If these folks can't do it even after years of training, you definitely can't either.