An individual in a trance appears to be in a sleeplike condition which is usually accompanied by an indifference to his objective environment and an amnesia to whatever occurs during the period that he is in this state. Trance has a more popular usage than a scientific designation. It can describe a daze state resulting from drugs, illness, prolonged contemplation, or other agencies.
Mystics can induce trances, or altered states of consciousness, by fasting, positioning himself in strained physical postures, and intense concentration. He becomes unaware of his physical environment including all physical discomfort which he may be experiencing. Instead he experiences deep emotional revelations or significance intellectual adventures.
Source: (Philip L. Harriman, Professor of Psychology, Buckwell University) 61.