Here’s what I know:
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For whatever reason, it’s impossible to breathe while doing this.
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it’s much easier to do it with your eyes closed.
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I’m pretty sure the roar isn’t blood because I can’t hear a heartbeat or any real change in the sound.
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Finally, whatever I’m doing makes my closed eyes vibrate.
I suspect what is happening is somehow I’m making my sinuses expand while my throat is closed.
Sorry if I sound insane.