Help Passing out from exhaling?

[boopboop]

I've been wanting to pass out without help, or materials, and I remember seeing something years ago about passing out just by exhaling. Pretty sure it was something about laying down and breathing out more then in and then you pass out. I was having trouble finding where I saw that though, and I need some help on time, like how long you're out/how long to get out etc. because I don't want to be found out if I do it. If someone knows about that I'd appreciate it if you shared