> don't breathe

Lack of oxygen immediately contributes to cognitive decline.

Only in the long-term (ie: more than 5 seconds). But for those initial seconds, you're a bit better off!

Swings and roundabouts. ¯\_(ツ)_/¯

Atmospheric nitrogen is a very mild anesthetic which reduces cognition. If we could replace nitrogen with helium in the gas we breathe then we would all be a tiny bit smarter.