I know a cultural anthropologist who researched the influence of drugs on trances used in voodoo rituals. Possession trances occur usually during rituals such as services or a vodoun dance in honor of the spirit. When spirits appear to tranced people, they may bring warnings or explanations for the causes of illnesses or misfortune. I've also read about how some witch doctors who had ingested drugs to induce trance states were assumed dead after the ritual, mistakenly or purposely buried alive, only to be unearthed so they could later tell the tale.
