If a character ever takes equal to or more than his Toughness in damage from a single hit, he starts dying. A dying character is unconscious and must make a DC 4 endurance check every round, with a -1 penalty for every wound the character has. Success means he gets to make another check next round. For every failed check, the DC increases by 1. If the DC becomes too high for the character to be able to succeed (ex., the character has Endurance 3 and the DC is higher than 9), then the character dies. If a dying character gets wounded while dying, he dies.
A dying character has a 10% (a roll of 10 on a d10) chance to stabilize each round. A stabilized character is still unconscious, but is no longer in danger of dying. A successful Medicine check can also stabilize a dying character.
If a character dies, a timely Medicine check, using Resuscitate, can bring character back to life.