Jewel of the North, formerly know as vincegetorix
A small tangent, but its really fun! But I disagree with the poster that its a solution for players who doesnt know the rules well enough. I do it frequently BECAUSE I know my character sheet like the back of my hand and have a solid grip of the rules. So, I can ask the Dm to cue me when my hp drops under bloodied (50% hp) and critical (within 1 hit of being dropped to 0 hp).Now this I've never heard of. It'd take a lot of trust in the DM, for sure, but I do find myself curious as to how this would look in play.
So yeah, clearly not for everyone, but I can assure you that its worth trying at least once.