So, my current reading. Tell me this doesn't sound like a sick joke: in the late 50s at the Ypsilanti State Hospital they brought together three people each suffering the delusion of being Jesus Christ and put them in the same room. (Actually, several rooms.)
It wasn't just they were curious to see what the three Christs would do. But that was part of it. They were interested in how people form their beliefs, with personal identity of particular interest because it's such a central one and it's so impossible to argue people out of who they think they are. And there were legends of people who had the delusion of being someone else being shocked out of it by meeting someone else with the same delusion. That didn't happen in this case; the Christs figured out ingenious reasons why they were right and the other putative Christs were just wrong.
Where it gets to the jaw-dropping, ``what were they thinking'', this is what the author apologizes for in the 1980s edition, part is: one of the men believed himself to have a wife (who, being a Yeti, was taken to be imaginary). They began writing letters pretending to be from her to see how far they could manipulate his behavior. You can actually feel --- at least, I can feel --- the researchers realizing that maybe this started out questionable but probably not harmful (maybe beneficial, since they were getting much more personal care than as part of a general mental hospital population) and then stumbled into ``what if anything were you thinking?'' territory.
It is all fascinating stuff, though I did feel like I was being callous when the men's monologues got to ... well, stuff that sounded funny. I mean, when someone claiming to be Jesus Christ says that several years ago besides his duties as God he was also governor of Illinois, it sounds like the sitcom representation of Zany Crazy People. But reading nearly 200 pages of this breaks past that impression. I got to feeling for the people afflicted and hoping for their health, even if they didn't come to thinking of themselves as their pre-Christ personas.
Trivia: Britain's King George III in 1804 attributed his 1801 mental disturbance to worry and concern about public affairs, particularly being called upon to break his coronation oath and consent to the emancipation of Roman Catholics. Source: George III, Christopher Hibbert.
Currently Reading: The Three Christs of Ypsilanti: A Narrative Study Of Three Lost Men, Milton Rokeach.