And that’s why, when you remove that critical 21% of oxygen, your body doesn’t realize it’s suffocating. You breath normally but pass out really quickly since your brain has nothing to burn.
Some reporter from Salon, or Wire - some big site like that - participated in a controlled nitrogen hypoxia experiment on himself, and wrote about it. It was really interesting, but search engines are flooded with that Alabama execution, and I lost interest in searching for it.