I've been thinking a little about this myself, but I don't have complete knowledge of the many mental disorders that Johnny's behavior might resemble. I figure someone here may have more knowledge and has an idea of what it could be, whether it's a real disorder or an exaggeration of one as seen in older media.

Regarding the latter, I do have somewhat of an idea of Johnny having multiple-personality disorder (the exaggerated kind you see in lots of fiction, like Split or Stargate SG-1, which can be misrepresentative) which may explain why Johnny, Zampano, and Pelafina's writing is all connected and similar to some extent. As for the Editor, I don't have a good answer. This is assuming Johnny is the main personality who has all the knowledge and put together everything written by the others, albeit with interference from Zampano and Pelafina. Johnny would have the knowledge to write everything in the book, but only retains some of it due to the personalities emerging and maybe how his brain works with that. However, Johnny may have more than just a personality disorder attributing to it. But this probably doesn't represent how the real-world personality disorders really work.

The Editor angle throws a wrench into some of the ideas, but with this one, I figured there's a possible way to explain it. Either the Editor is another personality or it's a more stable but not altogether Johnny adding in more details and evidence after-the-fact.

What do y'all think?