Causes or triggers include:
Falling asleep and waking: hypnagogic and hypnopompic hallucinations
Bereavement, in which hallucinations of a deceased loved one are common
Severe sleep deprivation
Extreme stress (see below)

Trauma and Stress
Traumatic life events have been linked with an elevated risk of developing psychotic symptoms. Childhood trauma has specifically been shown to be a predictor of adolescent and adult psychosis. Individuals with psychotic symptoms are three times more likely to have experienced childhood trauma (e.g., physical or sexual abuse, physical or emotional neglect) than those in the general population. Increased individual vulnerability toward psychosis may interact with traumatic experiences promoting an onset of future psychotic symptoms, particularly during sensitive developmental periods. Importantly, the relationship between traumatic life events and psychotic symptoms appears to be dose-dependent in which multiple traumatic life events accumulate, compounding symptom expression and severity. However, acute, stressful events can also trigger brief psychotic episodes. Trauma prevention and early intervention may be an important target for decreasing the incidence of psychotic disorders and ameliorating its effects.A healthy person could become psychotic if he is placed in an empty room with no light and sound after 15 minutes a  phenomenon known as sensory deprivation.Neuroticism, a personality trait associated with vulnerability to stressors, is an independent predictor of the development of psychosis.
EIS are specifically intended to fulfill the needs of patients with early-phase psychosis. In addition, one meta-analysis that consisted of four randomized clinical trials has examined the efficacy of EIS to Therapy as Usual (TAU) for early-phase psychosis, revealing that EIS techniques are superior to TAU.A study suggests that combining cognitive behavioral therapy (CBT) with SlowMo, an app that helps notice their "unhelpful fast-thinking" might be more effective for treating paranoia in people with psychosis than CBT alone. See also
Open Dialogue
Metacognitive training

References
Bibliography
Badcock JC, Paulik G, eds. (2019). A Clinical Introduction to Psychosis: Foundations for Clinical Psychologists and Neuropsychologists (1st ed.). Cambridge, Massachusetts: Academic Press, imprint of Elsevier. doi:10.1016/C2017-0-01829-3. ISBN 978-0-12-815012-2. S2CID 243510002. Lewandowski KE, Moustafa A, eds. (2019). Social Cognition in Psychosis (1st ed.). Cambridge, Massachusetts: Academic Press, imprint of Elsevier. doi:10.1016/C2017-0-03061-6. ISBN 978-0-12-815315-4. S2CID 239126550. Semple D, Smyth R (2019). "Schizophrenia and related psychoses". In Semple D, Smyth R (eds.). Oxford Handbook of Psychiatry (4th ed.). Oxford: Oxford University Press. pp. 179–240. doi:10.1093/med/9780198795551.003.0005. ISBN 978-0-19-879555-1. Tamminga CA, van Os J, Reininghaus U, Ivleva E, eds. (2020). Psychotic Disorders: Comprehensive Conceptualization and Treatments (1st ed.). Oxford: Oxford University Press. doi:10.1093/med/9780190653279.001.0001 (inactive 31 July 2022). ISBN 978-0-19-065327-9. {{cite book}}:  CS1 maint: DOI inactive as of July 2022 (link)
Thompson AD, Broome MR, eds. (2020). Risk Factors for Psychosis: Paradigms, Mechanisms, and Prevention (1st ed.). Cambridge, Massachusetts: Academic Press, imprint of Elsevier. doi:10.1016/B978-0-12-813201-2.00001-6. ISBN 978-0-12-813201-2. S2CID 213499429. Further reading
Personal accounts

External links

National Institute of Mental Health