Andrew Huberman· PhD
Now, of course you have to breathe sooner or later but what you'll find is if normally your ability to hold your breath is a minute or so before you really feel that gasp reflex kick in, you might find that you can go 90 seconds or two minutes. And with some practice, people find that they can start holding their breath for three or four minutes or longer. [...] And in fact, what you'll notice is that even though during that 25 or 30 breaths, [inhales and exhales quickly] you'll feel very alert, when you exhale all your air and you're in the breath hold, you will feel very alert, but very calm.