To categorize four types of sleep- and non-sleep-related hallucinations experienced by normal people and classify ghost or ghost-like stories by these categories. A total of 183 reliable tales of ghosts [41 from "Tohno Monogatari" (Tohno Folktales) and 142 from "Nihon Kaidan Shu" (Ghosts Tales of Japan)] are classified into hallucinations that are sleep-related hallucinations [hypnagogic hallucination-like (HyH) and REM sleep behavior disorder or somnambulism-like (RBDS) tales] and sleep-unrelated [vivid hallucination-like (VH) and highway hypnosis-like (HHy) tales] according to the criteria. Sixty to 70% of these tales can be classified into these four types of hallucinations. Further, sleep-related hallucinations increased from 17.0% to 36.6% in about 40 years. Our criteria will be useful to classify hallucinations experienced by normal people and to elucidate the mechanisms of these kinds of hallucinations experienced in neurodegenerative or psychological disorders.
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