When you are dying, you need to make a saving throw at the end of your turn each round. The result of your saving throw determines how close you are to death.
Lower than 10: You slip one step closer to death. If you get this result three times before you take a rest, you die.
10–19: No change.
20 or higher: Spend a healing surge. When you do so, you are considered to have 0 hit points, and then your healing surge restores hit points as normal. You are no longer dying, and you are conscious but still prone. If you roll 20 or higher but have no healing surges left, your condition doesn’t change.