One way I've thought of to help players of Barbarians to keep better track of where they stand is to factor those extra hit points into the unconscious and dead levels on your character sheet when you're raging. Eg. when your 10th level barbarian goes into a rage, instead of adding 20 hit points to his total and then taking them away when the rage ends, you could note that he's now disabled at -20 hit points, unconscious at -21, and dead at -30. That way, it would always be clear to you exactly where your character stands ... and falls. 
