The Origins of floatation therapy are attributed to the post-war research done by John C. Lilly. Lilly, a neuroscientist, was sure that dolphins had a superior intelligence and that humans could use it to add to their own. During the 1950's he developed what were essentially water-filled living areas where he and his research team could live alongside dolphins. During this time he even developed what he hoped would be a common language.
The 60's and 70's saw the research take a different turn, making the tanks smaller and providing researchers with sensory deprivation. Lily began experimenting with this reduced sensory environment to increase his abilities to communicate with the dolphins.
"During a session in an isolation tank constructed over a pool where dolphins were swimming, I participated in a conversion between the dolphins. It drove me crazy, there was too much information, they communicated so fast." Lilly is noted to have quoted.
It should also be noted that Lilly had many experiments involving LSD and Ketamine. These research topics, though interesting, are for another day. The effects of these sensory deprivation tanks, later to become what we now know as float tanks, were noted by Lily sans LSD and dolphins to induce a state of calm, reduce muscle tension and have great effects on the brain chemistry. The popularity of these tanks grew during the 60's and 70's with people accessing them for treatment of mental illnesses and the reduction of stress caused by "modern living". The 80's saw a reduction due to the uninformed ideas of how the AIDS virus spreads. Today we are seeing a resurgence in their popularity.