>>375895201
It's a little bit dangerous for long periods (like hours) so best not to let that happen while you're asleep. That pain you're feeling is hypoxia - part of your flesh dying from lack of oxygen from the low blood flow. Bruising is where the blood vessels break open and bleed under the skin, pins and needles are the nerves stretching and misfiring.
I would recommend loosening off your straps if you feel tired in vr. You probably won't be moving around lots when you're tired so they aren't at risk of flying off when you're like that anyway.