I understand that you are sometimes mentally ill and stress is no good for you but you can't stop people from talking. If they don't do it when you can hear they'll just do it when you can't hear instead. You need to grow a thicker skin.
However, that said, do you have a music system with big speakers? My upstairs neighbour used to be a dick. Treat his kid like shit, hit his woman, act hard. I would blast my music every time he walked into his flat. Rock music too. Used to drive him nuts.
Also, maybe you should stop smoking weed. In my experience it's no good for people with mental illnesses. The paranoia just seems to add to the stress.