He’s not crazy. He’s just written that way.
While brushing his theeth, Harold hears a voice. Harold hears a voice of a woman telling a story. The voice of a woman telling HIS story, as if he was the character of some book, what happens to be terribly annoying and problematic, and turns into something far much serious when a single sentence is said: “Little did he know that this simple, seemingly innocuous act would result in his imminent death”.