Altered States (1980)

In the basement of a university medical school, Dr. Jessup floats naked in total darkness. The most terrifying experiment in the history of science is out of control... and the subject is himself.

A research scientist explores the boundaries and frontiers of human consciousness. Using sensory deprivation and hallucinogenic mixtures from Native American shamans, he explores these altered states of cognizance and finds that memory, time, and reality itself are states of mind.