There are many causes of psychosis. They include too little sleep, some prescription medications, and abuse of alcohol or drugs like marijuana and LSD.
Traumatic events, like the death of a loved one or a sexual assault, can lead to psychosis in people who are vulnerable to it -- so can traumatic brain injuries, brain tumors, strokes, Parkinson’s disease, and Alzheimer’s disease.
Psychosis can also be a symptom of a mental illness, like schizophrenia or bipolar disorder.