What Hit Points Represent: Hit points mean two things in the game world:
the ability to take physical punishment and keep going, and
the ability to turn a serious blow into a less serious one.
At -10 or lower, you're dead.
Massive Damage: If you ever sustain a single attack deals 50 points of
damage or more and it doesn't kill you outright, you must make a DC 15 Fortitude save. If this
saving throw fails, you die regardless of your current
hit points. If you take 50 points of
damage or more from multiple attacks, no one of which dealt 50 or more points of
damage itself, the
massive damage rule does not apply.