I would not presume to speak on behalf of others, but my own personal opinion is that the very real and frightening demon attacks I used to think I experienced were the direct result of mind control tactics, and the power of suggestion on a vulnerable mind. I was being scared half to death week after week sitting through countless meetings warning about Satan and his demons being everywhere, looking for ways to get me. Stories of JWs being given gifts that turned out to have demons in them and the terrifying ordeals they went through trying to get rid of the things. No wonder I was paranoid and thought I saw and experienced things. As already mentioned, this is a tactic used by many religions to control their flocks, not just JWs.
It is amazing how, since realising these things do not actually exist, I have never had any problems at all. I can read whatever I like, watch any film, buy antiques and pre-owned items without needing to find out who owned them before me and the worry that they might be demonised.
It's great to be free