Psychological explanation for exorcisms?
Google Scholar reveals a substantial quantity of learned research on the topic of exorcisms, of which the items below are but a few:

Ferracuti, S., &amp; Sacco, R. (1996). Dissociative trance disorder: clinical and Rorschach findings in ten persons reporting demon possession and treated by exorcism. Journal of personality assessment, 66(3), 525-539. https://doi.org/10.1207/s15327752jpa6603_4

Ross, C. A., Schroeder, E., &amp; Ness, L. (2013). Dissociation and symptoms of culture-bound syndromes in North America: A preliminary study. Journal of Trauma &amp; Dissociation, 14(2), 224-235. https://doi.org/10.1080/15299732.2013.724338

McNamara, P. (2011). Spirit Possession and Exorcism: History, Psychology, and Neurobiology [2 volumes]: History, Psychology, and Neurobiology. ABC-CLIO.

Henderson, D. J. (1976). Exorcism, possession, and the Dracula cult: A synopsis of object-relations psychology. Bulletin of the Menninger Clinic, 40(6), 603.

Bull, D. L. (2001). A phenomenological model of therapeutic exorcism for dissociative identity disorder. Journal of Psychology and Theology, 29(2), 131-139. https://doi.org/10.1177/009164710102900204

Pfeifer, S. (1994). Belief in demons and exorcism in psychiatric patients in Switzerland. British Journal of Medical Psychology, 67(3), 247-258.  https://doi.org/10.1111/j.2044-8341.1994.tb01794.x

Rosik, C. H. (1997). When discernment fails: The case for outcome studies on exorcism. Journal of Psychology and Theology, 25(3), 354-363. https://doi.org/10.1177/009164719702500304


As for many religious behaviours, exorcism behaviours appear to exist between non-intersecting religious and cultural groups.
A review of the abstracts suggests that involvement in exorcism is considered to be a Dissociative disorder.  The Mayo Clinic also has an interesting article on Dissociative disorder.