A character with 0 hit points, or one who has negative hit points but has become stable and conscious, is disabled. A disabled character may take a single move action or standard action each round (but not both, nor can he take full-round actions, but he can still take swift, immediate, and free actions). He moves at half speed. Taking move actions doesn't risk further injury, but performing any standard action (or any other action the GM deems strenuous, including some free actions such as casting a quickened spell) deals 1 point of damage after the completion of the act. Unless the action increased the disabled character's hit points, he is now in negative hit points and dying.
A disabled character with negative hit points recovers hit points naturally if he is being helped. Otherwise, each day he can attempt a DC 10 Constitution check after resting for 8 hours, to begin recovering hit points naturally. The character takes a penalty on this roll equal to his negative hit point total. Failing this check causes the character to lose 1 hit point, but this does not cause the character to become unconscious. Once a character makes this check, he continues to heal naturally and is no longer in danger of losing hit points naturally.
Marius, Scholai Armsmaster Says: One hour after a character becomes stable (and each hour thereafter), they receive a DC 10 Constitution check to wake up with the disabled condition. This means that a heavily damaged group will eventually be able to limp away from a battle without having to drag a pile of unconscious allies behind them.