Towards the end, some stuff on the reality of dreams and the dreamworld (citing Sandman). Yes that is the interesting question. Not so much as to whether the dream world "exists", it obviously does in some abstract way, in that we can refer to it as well as visit it. More, "what is the nature of this world's being and how does that relate to the mundane variety of being?"
Burrough's Portugese Mooch. Must be some other good literary interpretations (Loki in Sandman? But too fucking obvious about it). Rage is not very interesting unless it carries a risk of real violence along with it. Saleri. Malkovich in Burn After Reading, a very wimpy, silly sort of rage but real enough.
I've been a longtime fan of the Neil Gaiman graphic novel. I still like to reread it, even though its narrative games seems a bit klunkly and childish to my older self, I still like to see the machinery work. Looking forward with mixed feelings towards the upcoming TV series.
Sandman is centered around the figure of Morpheus aka Dream, one of the seven Endless siblings who are somewhat more than gods, more like fundamental metaphysical structures, anthropomorphized for your entertainment. Dream rules not only sleep but stories and the imagination in general, making him a natural stand-in for Gaiman himself, and there quite a bit of riffing on the status of the fictional and its relationship to reality.
Interestingly parallel with Promethea, by the other genius-level English graphic novel author, Alan Moore, which is also explicitly about the imaginal.
Another parallel: the last half of the Sandman run involves (spoiler) the death of Dream, because the Endless can die and there is even some metaphysical machinery to handle it (see the Litharge story in World's End). Recall's that line in Watchmen "I shall go tell the indestructible man that someone plans to muder him"