"MORTALLY WOUNDED" "INCAPACITATED"

When you drop below 0 hitpoints, you will enter one of these two states or
DEAD if low enough.

Incapacitated means you will regenerate back to conciousness (positive hp)
if nobody kills you.  Aggressive mobs will normally keep attacking you even
when incapacitated.  Some mobs will stop fighting though.  The threshold
for this state is your level / 4 (or -10 at a minimum).  So if you are level
60 then the threshold is -20.  In addition you get 15 more hp of range
for each rank of toughness you have.

Mortally wounded means you will slowly bleed to death unless someone heals
or binds your wounds.  The threshold for this is level / 2 (or -15 at a
minimum).  Toughness ranks also add 15 more hp of range per rank.

The threshold for death is -level (or -20 minimum) with similar bonus for
toughness.

See also: DEAD, TOUGHNESS