The term idionecrophany comes from the Greek words idios (private, one's own), nekros (dead), and phainestai (to appear). It was proposed in or shortly before 1992 by the American sociologist William L. Macdonald to denote any sensory experience involving a claimed contact with the dead. The term was introduced to solve the dilemma of having to choose between labelling such experiences as hallucinations or " apparitions (in the sense of spectres or ghosts).
References
Macdonald, W.L. (1992). Idionecrophanies: The social construction of perceived contact with the dead. Journal for the Scientific Study of Religion, 31, 215-223.
Dictionary of Hallucinations. J.D. Blom. 2010.