In the last book, one of the characters was put in a situation to half/half by accident/by coersion murder someone he cared deeply for, essentially a love interest he had taken to protecting. He did so in order to save thousands of people, but still, he ended up killing someone he cared about. At the end of the book he spirals into depression and apathy, and goes off on his own to live in misery and guilt.

Given that background, would you as a reader believe it if he started having hallucinations of the woman he murdered? Both as a combination of guilt and loneliness as he isolates himself, to have someone to talk to, and also as a way of "beating himself up" but having a vision of this woman tormenting him basically all the time?

Also, is it possible under these psychological depression hallucinations to not, say, hallucinate about all sorts of stuff, but have this single focused hallucination in the form of a person, but to be completely "normal" in your other perceptions?

Think of the movie "A Beautiful Mind" where the MC realizes that 3 people in his life don't exist, and gets past his disease by simply accepting that fact and ignoring those hallucinations. I suppose that illustration just answered my question actually. I certainly "bought it" in that movie, I accepted the premise... so I think I'll feel free to toy with this idea in my novel.

For example when I worked my psychaitric ward as a student I remember talking to a guy who seemed completely sane and reasonable. I spoke to the nurse in charge and made the same point. She suggested i question him on a particular topic (What color his skin was--he was white) and it became obvious the guy had this fixed, immovable (well, immovable without some hefty anti-psychotic meds, anyway) delusion that he was a black guy.

As regards treatments in the middle-ages; Tre-panning (boring holes in the skull to let out the spirits; treated using extracts like valerian, perhaps to calm people, St. John's Wort etc.(I am no herbalist so you will have to check that stuff--I am guessing); hanging or burning them as they are possessed by evil forces (death--quite an effective treatment!); dunking in water; beating (You may think twice about telling people about your hallucinations if they do that to you when you do); kicking them out of village to fend for themselves (Darwinism).

All pretty basic stuff--but off the top of my head--you'd probably want to confirm some of those ideas with a bit of research.

Adam

How will your "hallucination" treat your MC? Will the hallucination be his attempt to pretend/wish she hadn't died (and be loving like she was), or will she be his way of punishing himself (angry at him - maybe she "makes" him step in front of cars or something)? Perhaps she could start out angry and eventually forgive him (as he learns to forgive himself).

Basically, visual hallucinations post-trauma kind of suck.

Unless he were on drugs, in which case I'd expect him to see stuff that wasn't there. But then, why would the guy take drugs that make you hallucinate (cannabis, LDS), if they bring back painful flashbacks? Unless he's punishing himself for what he's done, in which case you've got a powerful self-destructive psychological tool there.

Normal psychotic hallucinations are usually heard, rather than seen (ie: voices, not ghosts). But hey, if he's depressed and drinks a lot then yes, visual hallucinations could come about, both as a result of repeat pathological intoxication or deprivation. It would still be very weird, but the Medical bone in me won't be screaming for mercy.

Another possibility is PTSD: he wouldn't see things, per se, but he'd have constant flash-backs of the episode, nightmares etc. He'd be aware that this stuff wasn't real, but he wouldn't be able to stop it.

Yet another way of doing this: he's seeing her actual ghost. He puts it down to hallucination, until someone tells him that that is really really weird and that, hmmm, maybe if you see a ghost, it is a freaking ghost.

Could some kind of combination of severe depression coupled with like withdrawl symptoms of lack of alcohol or something like that possibly cause hallucinations? Coupled with PTSD?

Obviously, since this is a fantasy story in non-modern times, none of these terms are going to make their way into the story itself, but I do want to try to show the circumstances in a realistic way.