one's own demonic possession (delusional conviction).
pathological belief that one is possessed by demons
• (n.) A form of madness in which the patient conceives himself possessed of devils.
De·mon`o·ma'ni·a noun [ Demon + mania .] A form of madness in which the patient conceives himself possessed of devils. 
daemonophobia, demonomania An intensive fear of demons (spirits, goblins, etc.).demonomania A morbid dread of being possessed by demons.