Characters are unconscious at 0 HP, and every turn they are at 0 HP or lower they must save versus death at -1 for every point they are below 0 HP or die.
If the character survives and another character applies first aid successfully to the incapacitated character (spending a turn binding wounds, staunching bleeding, etc.) then the incapacitated character is returned to 1 hit point and will regain consciousness in 1d6 turns.