Cotard Delusion
https://en.wikipedia.org/wiki/Cotard_delusion
The Cotard delusion (also Cotard's syndrome and walking corpse syndrome) is a rare mental illness in which an afflicted person holds the delusion that they are dead, either figuratively or literally; yet said delusion of negation is not a symptom essential to the syndrome proper.[1] Statistical analysis of a hundred-patient cohort indicates that the denial of self-existence is a symptom present in 69% of the cases of Cotard's syndrome; yet, paradoxically, 55% of the patients present delusions of immortality.[2]
[The patient's] symptoms occurred in the context of more general feelings of unreality and [of] being dead. In January 1990, after his discharge from hospital in Edinburgh, his mother took him to South Africa. He was convinced that he had been taken to Hell (which was confirmed by the heat), and that he had died of septicaemia (which had been a risk early in his recovery), or perhaps from AIDS (he had read a story in The Scotsman about someone with AIDS who died from septicaemia), or from an overdose of a yellow fever injection. He thought he had "borrowed [his] mother's spirit to show [him] around hell", and that she was asleep in Scotland.[9]