I knew of a very odd brother that used to do a lot of street witnessing on his own, I guess no one would work with him. He was disfellowshipped, so I asked my dad why, he said because he heard voice, so they knew he was inviting demon attacks. I asked my father if he could just have been schizophrenic, he said no, it must be demons. This was a long time ago, but not so long they couldn't have know hearing voices was a sign of mental illness.
I was also thinking about my daughter, who had mental issues as a teen, eventually she was diagnosed with borderline personality disorder (she's fine now though). If you didn't know her well you might think one of her meltdowns was a demon attack, she would go from normal to out of control meltdown very quickly, say very alarming things, cut herself, etc. It was really, really scary. I wonder how many JW teens with borderline personality disorder have parents who think they are demonized?