So here is my final go on the system. I've changed the overall thought to that of mortal wounds and changed some of my assumptions (a very unlucky PC can die before reaching -10 hp for example). Note that the following house rule replaces the rules for what happens to any creature when an attack brings them below 0 hp. Zero and above hit points follow the normal rules for all creatures (including constructs and undead being destroyed at 0 hp).
Mortal Wounds: Any hit that brings your hp total below zero is a mortal wound. Roll on the appropriate chart for the type of weapon as follows (this replaces normal rules for falling below zero hp):
-1 to -10 hp Column A
-11 to -20 hp Column B
-21 to -30 hp Column C
-31 to -40 hp Column D
-41 to -50 hp Column E
-51 or lower hp Column E + Column C
Effects:
Hits = Additional hp of damage, makes you more vulnerable if attacked again and harder to heal.
Rounds of stun = drop everything held, can’t take actions, take a -2 penalty to AC and lose Dex bonus to AC.
Rounds of no parry = drop to the ground helpless, only action available is to crawl 5 feet per round.
Rounds of must parry = dazed.
Hits per round = continuous hp damage until healed.
Penalty = divide penalty by 5 to determine penalty to attacks, skill checks and ability checks.
Bonus = divide bonus by 5 to determine bonus to attackers attack rolls.
Other effects occur as described in the table entry.
The effects persist for the indicated number of rounds. After that you may function as normal. Instant death results are unavoidable. Death that occurs in a number of rounds may be prevented by healing that brings you out of negative hit points. Effects that do not list a specific number of rounds persist until you are brought back to zero or more hp.
Charts used: 4.1 Brawling (unarmed strike), 4.2 Grappling, 4.3 Krush (bludgeoning), 4.5 Martial Arts Strikes (improved unarmed strike), 4.6 Martial Arts Sweeps (improved trip), 4.7 Puncture (piercing), 4.8 Slash (slashing), 4.9 Subdual (any non-lethal attack) and from Spell Law, 10.81 Heat (acid or fire), 10.82 Cold, 10.83 Impact (force, sonic or un-typed), 10.84 Electricity.
Permanent bodily harm can be corrected with Heal, unless a body part is severed which then requires Regenerate.