You don't lose the game for having 0 or less life.
When you have 20 or more life, you lose the game.
Whenever you lose life, you gain 2 life for each 1 life you lost. (Damage dealt to you causes you to lose life.)
10/4/2004 If your life total is 20 or more and you control an effect that states “you can’t lose the game”, then an infinite loop is formed. If neither player wants to end the loop by removing one of these two cards from the battlefield, the game ends in a draw.