I think it is important to note that people involved in a mass hysteria event are typically
not mentally ill, or even enduring a "strange mind state". When dealing with mass hysteria as it relates to
ghosts, it is also important to know that many people use the term "mass hysteria" improperly. The quote in the OP:
Skeptics use the term "mass hysteria" for situations like this, but nobody has offered an explanation for the core catalyst causing many brains to suddenly go haywire.
...seems to (possibly) imply that the author thinks "skeptics" insist that "mass hysteria" causes people to hallucinate; to see or hear things that aren't really there. If this is a "the skeptics are wrong" argument, it would at first glace seem true - it's highly unlikely that a large group of people would share the exact same
hallucination. However, if somebody is using the term "mass hysteria" properly in a context involving ghosts or hauntings, that would
not be the case. A group of people inflicted with mass hysteria would not experience "communal hallucinations"; they would simply interpret (or remember) normal or natural events in a bizzare or irrational - and typically erroneous - fashion. The suggestiblity of the group may have been
brought on by a person or persons (the catalyst) which did experience hallucinations.
I've got another example of mass hysteria, which happens to be my personal favorite. Although not nearly as famous as the Salem trials, the "satanic ritual abuse" (SRA) mass hysteria event of the 1980's had - and has - effects both farther-reaching and longer-lasting. It was also extremely complex, with several smaller "instances" of mass hysteria both drawing on an fueling a nationwide epidemic.
It started (arguably) with Anton LaVey establishing the "First Church of Satan" in California. LaVey was a person who really did not like Christians, and he set up his church to spite them. He and those who joined his church held "black masses" which lampooned Christian services, and he wrote a book called "The Satanic Bible" which really had nothing to do with Satan. However, the idea of "Satanism" had long been tangled with the ideas of ritualistic sacrifices and all that jazz; so when local media outlets began interviewing LaVey and self-proclaimed "Satanists" (there was one or two in every major city), people helped along by fear-mongering religious groups got the impression that Satanism was a huge thing, and that there were "hundreds of thousands" of Satanists everywhere. Rebellious high school kids started dressing in black and sacrificing squirrels and such, making up their own ceremonies.
It's uncertain exactly when it happened, but a some point a couple of disturbed young women, with help from "recovered memory" therapists, began describing horrible abuse at the hands of a "Satanic cabal". They were used for sex, beaten, scarred, and everything-else'd. After a couple of news stories, other women began "recovering" similar memories. Nevermind that the overwhelming majority of these women had no scars (or else the scars were surgical artifacts and the like), or were virgins (and so
probably weren't used for sex); the public digested all of it. The catalyst (the "exposure of Satanism") led to the mass hysteria atmosphere. Then, a second catalyst
within the mass hysteria bred a worse atmosphere - one of the women claimed to be used as a "breeder", who was made pregnant over and over again simply for the purpose of having children to be used in sacrificial rituals. That accusation opened up a whole 'nother can, and outrageously stupid "facts" (like the assertion that literally
millions of children in the U.S. were sacrificed every year in satanic rituals!) were accepted without a second thought.
The "climax" (as I see it) of all this was the infamous McMartin Preschool Abuse debacle, which remains the most expensive criminal trial in American history. It happened in Florida. A rather unbalanced woman leveled accusations of abuse (her son being the victim). "Experts" in recovered memory were brought in, and through gestapo-like interrogation of the other kids eventually gleaned a few stories of sexual abuse (involving, coincidentally, such elements as "turtles, rabbits, lions, a giraffe, a sexually abusive elephant, dead and burned babies, dead bodies in mortuaries and graveyards, goat men, flying witches, space mutants, a movie star, and local politicians"). Prosecutors and therapists recovered enough "memories", discounting all the ones that sounded too incredible, of course, to hold a
two and a half-year long trial. Cooler heads prevailed and the two defendants (the owner of the preschool and her son) were finally acquitted after having spent the entire duration of the trial in jail. Despite this, there's still a lot of pissed-off parents and some unfortunate children who now really believe they were abused in "underground tunnels" and secret rooms that never existed. For more information than you ever wanted to know about McMartin,
go here.
The beautiful failure of the McMartin trial (and similar trials in other locations) killed (for the most part) the SRA hysteria in the U.S., and although there are still accusations and fear-mongers, the phenomenon is not nearly an epidemic of the proportions it once was.