Breathing and then blowing your hand to faint

[fall]

Hi,

I know this trick, I don't know if it's common knowledge but it's fun and easy, and feels really weird (everyone should try it at least once).
Stand up, and then get down to the floor (keep your feet on the ground). I don't know how to call this position as English is not my native language. Just try to get your head between your knees or something. Then what you do is breath in and out as deeply as you can. Fill your lungs completely as fast as possible and then let go. Do this 10-20 times.
Then get up, and put the back of youyr hand to your mouth, ans start blowing as hard as you can, without actually letting the air escape (that's why your hand is there, to prevent the air from getting out). Keep blowing.

Normally, you will loose consciousness while blowing. It's a good idea to have someone to catch you as you might hurt yourself on your way down. Within a few seconds you will regain consciousness and it feels pretty weird, especially if you have consumed some alcohol beforehand.

Now, for my question. This can't be good for the brains, that I know. But exactly how bad is it? Is it like drinking a glass of bear? Or an entire night of drinking? Or even worse? I've done it on a few occasions, and was wondering how much I had damaged my brain with this trick.

Thanks for your answers.

[Richard Pearse]

Why put your hand to your mouth? Can't you just keep your mouth closed?

[fall]

dunno, someone tought me to do it like that, I've asked myself that question but never tried. but I think it might be too hard to keep your mouth closed when blowing very hard (can't try, I'm at work )

[Eleusis]

Hmmm I thought I remembered a Cecil column or staff report discussing this but I can't find it.

IIRC the danger was more one of immediate death, than one of lasting brain damage.

[raygirvan]

You're talking about the "Valsalva Maneuver". Exhaling against resistance causes circulatory changes, described at the above link, that can make you faint.