Fascinating! People are hallucinating because their immune system has produced an antibody against the NMDA receptor in their brain.  So many immune illnesses are present in people who have mental illness. Now it’s  being found that in many cases there is a connection

http://www.bbc.co.uk/programmes/b07pj2pw

BBC health reporter James Gallagher explores the increasing body of evidence that a dysfunctional immune system is responsible for the depression or psychotic illness experienced by hundreds of thousands, perhaps millions, of people in the UK. James talks to the psychiatrists investigating this new understanding of mental illness and to people who may benefit from treatments aimed at the immune systems rather than their brain cells.
“I believe this is one of the strongest discoveries in psychiatry in the last twenty years”, says Professor Carmine Pariante of his and other research on the immune system and depression. “It allows us to understand depression no longer as just a disorder of the mind and not even a disorder of the brain, but a disorder of the whole body. It shifts conceptually what we understand about depression.”
James also talks to New York journalist Susannah Cahalan. She began to experience paranoid delusions and florid hallucinations when her immune system made damaging antibodies against part of the molecular circuitry in her brain. Treatment to eliminate the antibodies prevented her committal to psychiatric hospital. Psychiatrist Professor Belinda Lennox at the University of Oxford says she has evidence that a significant proportion of people presenting for the first time with psychotic symptoms are victims of a similar autoimmune problem.