"Would you like to know about my unpredictable complications?" This is obviously a rhetorical question-- "I'm forced to keep my position indefinitely, the war starts again, and I die. I'm fairly certain, actually, that you're older now than I'll ever be. And I don't give a shit about it."

He's dead already and living on borrowed time. If hell is real, it's in no hurry to collect Severus Snape; he wonders if there'll ever be a time when he thinks about life after everything. He wonders what that fantasy would feel like. He's not capable of imagining it.

"Maybe I'll wake up different. Dead, or waiting a handbreadth before it like Petrelli. I suppose you could ask me what's wrong, then."

It'd be that he woke up at all.