Joe the Barbarian by Grant Morrison
Joe, imaginative eleven year-old orphan suffering from Type 1 diabetes, can't fit in at school. One fateful day, he enters a vivid fantasy world in which he is the lost saviour of a fantastic land based on the layout and contents of his home. But is his quest really just an insulin-deprived delirium, from which he can die if he doesn't take his meds, or something much bigger?