In my opinion, it's these two points here that make me 100% sure that the Institution was the delusion.
Buy given that there are things that have happened on both shows that Buffy has no knowledge about - Darla's resurrection, Jasmine and many, many others - to me, that shows that Buffy couldn't have imagined those things. There would be no need for her to create Fred or Gunn or Connor or to give Harmony a job working for Angel. None of them matter to her delusion as it affects her. They play no significant part and if she had wanted to get rid of Angel, Cordelia and Wesley from her immediate world, she could have simply killed them off instead of coming up with yet another delusion.
Exactly. Speaking once again hypothetically supporting Sunnydale as the delusion, I am wondering now if Buffy didn't in fact banish Angel but rather he was sent away either by brainwashing into her that he left or by medications. The conversation Joyce has with Angel in 'prom' fits in with this, Joyce could have been trying to say those things to the shut down Buffy in the institution and they came through to her as Angel being the recipient, as Joyce telling Angel to go away. Angel was her strongest delusion which she clutched most closely to her. So I could see them theorizing that getting rid of Angel might bring her back.
But Buffy continued to see Angel even after he 'left' which could have been her way of trying to bring him back but medication continued to block him. Such as when he appeared to prevent her death by the Native Americans but she never knew he had been there until Xander blabs and when she had visited him in his series and talked about how he could have been what she needed if he were human and for a time he had been made human but she is made to forget that.
Despite however there is no explanation for Buffy to create events for Angel in a separate world such as giving him a son and especially with Darla and all the hints of an Angel/Cordelia relationship. The entire idea that both Cordelia and Wesley after being banished from Buffy's world became stronger characters in Angel's makes absolutely no sense.
The other reason I don't buy into the delusion is Dawn.
In the delusion, Buffy is an only child, but in the comic, Slayer, Interrupted, which is largely considered to be canon by a lot of the fandom, the reason for Buffy being sent to the institution was because Dawn found her diary and told Joyce what was in it.
This ties into the actual show and explains why Joyce didn't mention that time when she found out the truth in S2 - because Dawn hadn't been created yet, so, neither had those memories.
Now this is interesting. I do not know this comic but if it is considered cannon by Joss than it does explain that angle. So Buffy having been institutionalized in Sunnydale world technically had not actually happened since Dawn was the direct cause however it was at a time when she wasn't actually there, it's a part of what was rearranged in memory to falsify that she was.
I however do not see this storyline fitting into the series because Buffy has never been shown keeping a personal diary (unless my memory is failing here), only the one she had to keep for the egg assignment in
Bad Eggs. It doesn't seem very Buffy but it could have also been something else that only occurred in the Dawn illusion of that time period.
There however also was the story Buffy told Willow in the episode, that she had been institutionalized because she herself went to her parents terrified of vampires. It was nothing to do with a dairy and Dawn was actually never mentioned. It was a completely different version that does not match this comic story line.
So though I have not read it, I already don't give validity to this comic.
I don't know if the institution reality was just an AU that the demon venom projected into Buffy's mind, or if the venom actually just made her imagine the whole thing. I like to think that it is an actual alternate reality, mostly because I like the idea of all these different versions of the characters are out there. Plus, there's a world without shrimp, I just think that's cool, lol.
The event of Joyce discovering the slayer persona of Buffy with Dawn vs. without if it fit better with the tv series would give it an alternate reality feel however what isn't clear is what made Buffy lie about the "delusions" being gone to merit her release in Sunnydale vs. the Institution reality where she clung to it as a manifestation of schizophrenia? What exactly is the difference between the two institution scenarios? Was it the level of reality the slayer persona had in each? What event had created the institution Buffy?Schizophrenia can either be genetic or can be brought on by environment which could mean anything from what the fetus is exposed to in the womb to social interaction, home life, viruses, drug use or stress. In Sunnydale-verse Buffy had been a popular cheerleader airhead prior to be chosen as the Slayer, was this different in the universe where she had been institutionalized from around that same age (or so it was implied)? What had her home and social life been before?
This is why Sunnydale being the delusion is barely supported, the schizophrenic Buffy wasn't developed leaving the more plausible question the one you presented. Did the demon's injection intentionally create the institution resembling an episode of
Charmed or was that scenario Buffy's individual response to it?