In 1919 the Hungarian psychoanalyst Sândor Ferenczi (1873-1933) defined hallucinations as follows. "A hallucination is brought into being when an affect-laden thought complex is blocked by the censorship on its progressive path towards consciousness, and the excitement emanating from it, taking a retrogressive-regressive path, re-occupies the thought's mourning material cumulated in the mind, allowing it to become conscious as an actual percept."
References
Ferenczi, S. (1919). Hysterische Materialisationsphänomene. Gedanken zur Auffassung der hysterischen Konversion und Symbolik.In: Fer-enczi, S. (1964). Bausteine zur Psychoanalyse. Band III: Arbeiten aus den Jahren 19081933. Zweite, unveränderte Auflage. Bern: Verlag Hans Huber.
Dictionary of Hallucinations. J.D. Blom. 2010.