I've done something similar.
Head between knees, rapid breaths, suddenly stand up and suddenly hold breath.
Overoxygenate the brain, then oxygen starve it - it'll either get you high, or make you pass out. As you said - good way to relieve boredom... also as you said, bad to have hard objects behind you. I discovered this on a coffee table. Bad way to fall.
However, I did discover (since that was the first time I'd ever been knocked out) that I'm perfectly conscious when unconscious, I'm just totally disassociated from my body. Very interesting experience - one of my most memorable mind-altering experiments. The sensation of no body and no spatial realm is quite fascinating. Everything black, but there is no black - colours don't exist... no eyes. And so on.
Not recommended for people with a family history of epilepsy. Can cause temporary amnesia and other nasty side effects (seen it happen, not pretty).
I can see why you'd want to use it for that purpose, but it's not a safe thing to do to your body. Can cause blood clots in the brain if done too much.