Occurrence of Altered States of Consciousness: An Overview

The article presents a comprehensive review of literature on the occurrence of altered states of consciousness. Only few studies directly aim at the estimation of occurrences of altered states of consciousness, therefore indirect studies are also included. They present data on the frequency, in normal populations, of such phenomena as: hallucinations, peak experiences, mystical states, hypnotic-like experiences, out-of-the-body experiences. In general, presented frequencies suggest that such phenomena are rather common. However, the author emphasizes the lack of any other clear conclusions from the existing data and expresses the need for further empirical research.