True. Even if upon witnessing such absurdities he had immediately assumed he was seeing things and demanded to be checked into a mental hospital, he couldn't even be sure that there was really anyone around him to hear, or that he was really saying what he thought he was saying, etc.

But then, if he's that far removed from reality, whatever he's really doing must appear crazy enough to draw the attention of those around him. Maybe he's already in a mental institution... which he imagines to be a school of wizardry! From the inside, he already sort of feels (and acts) as though he's the only sane person in a madhouse... while in reality, he's just another patient.