I have been wondering about marginal vitamin B12 deficiency as a cause of psychosis. About a year after I got sick, I had abnormalities with my RBCs, but the doctor shrugged it off because my hemoglobin was within normal range. My ferritin was low at 7. It sounds like a possible explanation and why I recovered. The year before I got ill, I was depressed and could barely function. Eating wasn't a priority. I never sought help, because I had no doctor at that time.
I asked my psychiatrist about medication causing psychotic symptoms. She stated they can cause delirium. This makes me wonder about the differences between the two.