One area of the prison I work in has this one particular inmate that seems totally normal most of the time. The problem is, when he is crazy, he is really crazy and you never know when his crazy will show up. He is known for being a drug abuser so all we can figure is that either the drugs caused this, or this caused the drug use. Either way, it can be interesting.
One day you will be interacting fine with him and the next, his crazy comes out. You will come in to work and he will be having an issue with someone and call you over. That's when you realize things are not normal for him. He will tell you all about how all the other inmates are urinating on him and he needs you to get them to stop. Next thing you know, he is convinced that you are urinating on him as well and he looses it. The poor guy is completely convinced that the whole world is peeing on him! Imagine that... well, maybe don't imagine that as that would be a little too graphic but you know what I mean.
Because this is all in his head, nothing you or anybody else says will convince him that you aren't peeing on him. So he ends up being sent to seg until he returns to normal then he forgets it ever happened and moves on. The inmates on the other hand, they have a tougher time forgetting it.