One vital difference between fifth-century Greeks and “us” (or the range of job-lot attitudes which that word represents) is that in their world seeing gods, coming into direct contact with divinity, was not evidence of madness. Or not in the way it is in ours. Our world generally tends to think seeing gods is evidence of madness because it is hallucinatory, because gods to not exist. “He’s been seeing things” means precisely the opposite. He has not been seeing things; not things that are really there. He has been making them up, “seeing” creations of his own disturbed imagination.

But the plays that stake out the claims of madness on Western imagination were produced for the precinct of a “mad” god. A real god, really present in “his” theatre. Dionysus’s persona connected interior violence, the violence of the mind and distorted perception, with exterior violence: the violence of tragedy’s action, its music, dances and murders. Seeing Dionysus was evidence of seeing Dionysus. That might well mean madness, not because Dionysus was not real, but because he was.

"Whom Gods Destroy": Elements of Greek and Tragic Madness, Ruth Padel (via paperquake)