I can relate to what he is going through. I was diagnosed years ago as schizoaffective. But I was also in a major depression that was untreated, which can also cause delusions.

Anyway when I am under alot of stress I become very paranoid. I begin to think that people are doing things "on purpose" to hurt or humiliate me. When this first happened to me I thought my home was bugged and people were watching me. Like your co-worker.

You are right to keep gently recommending that your co-worker go get professional help, a psychiatrist especially to get him on some appropriate meds to help him through this time. Of course I can tell you it's very tough to accept help when you are feeling this way. I feel I can't trust anyone. It's not so bad for me anymore as I have learned to get help, therapy, meds, and just how to deal (ignore) with those paranoid type thoughts. But I find if I have too much stress in my life - which for me isn't much at all compared to most people - the paranoia really kicks in and makes life hell for me and those around me.

If you can continue to be gentle, understanding and kind but insistent that his paranoia is a sign that he needs professional help and medication, it might be helpful to him. Perhaps a small group of co-workers, who are truly concerned and can communicate this to him, can try approaching him in a nonthreatening way.

Does he have family that you (or someone in an appropriate position at work) can contact? This might be something to try also, let them know how concerned you are about him and his paranoid symptoms.