What does the skull mean on your point card in the heal points? It goes to 12 and then the next is a skull.
The skull is actually indicating 0 Life Points (i.e. you are dead and eliminated from the game). This is made more explicit in the Fifth Anniversary Edition rules:
In other words, the skull is one lower than 1 Life Point rather than one higher than 12. The fact that the skull and 12 are next to each other is only because this is a round wheel.