EFFECT ONE -- Violence. Characters become aggressive to the extreme--not just threatening violence, but actually going through with it. They will lash out first and never ask questions at all; the smallest thing could set them off. They won't stop, either; they'll just keep going until they're stopped. People under this effect are much more twitchy and nervous.
EFFECT TWO -- Passive. These people have become suddenly super-dependent and needy. We're not talking just about co-dependent partner-types, here; these are people who suddenly literally need the approval of everyone, and are willing and desperate to do whatever they can for attention and affection. They want to be loved and admired and noticed, and they may latch onto one person, or to a group of people, or anyone passing by might do to give them their "fix" for attention. They are clingy and afraid, and they need your comfort right now.
EFFECT THREE -- Manipulation. "The innocent cruelty of children"--only there's nothing so innocent about this. A lot of it's rather deliberate and rather unkind; it's schadenfreude taken to an extreme level. Offer to do something, only to laugh in their faces when they're grateful. Push someone down the stairs and pretend you saw nothing. It doesn't matter, as long as it's funny.
EFFECT FOUR -- Denial. Everything is fine, peachy keen! In fact, maybe you have never felt better. No matter what methods people take to try and get through to you, and show that things are really not great, and really not normal, it's not going to take.