The first sensory deprivation tank was designed in 1954 by John C. Lilly, an American physician and neuroscientist. He wanted to study consciousness by removing external stimuli. His research soon became problematic as he used it for experiments on subjects using hallucinogens and other drugs. His tanks were tried by Richard Feynman, Nobel Prize winning physicist, who discussed his experience with isolation tanks in his book Surely You’re Joking, Mr. Feynman! “I realized that other people had found the sense-deprivation tank somewhat frightening, but to me it was a pretty interesting invention. I wasn't afraid because I knew what it was: it was just a tank of Epsom salts.”
The tanks contain water heated to skin temperature and filled with epsom salts. The salts are measured into the water to create specific gravity of approximately 1.275. This gives you the sensation of floating without effort or awareness of the water around you. The tank is dark and soundless, though in modern float spas, you can also play relaxing music and have coloured lights.
For many people, floating is a method of meditation. Zach Palmarin, owner of Tranquility Float Centre in Lethbridge, says, “not only could I meditate in the tank, but I also discovered a wide universe of benefits. I found I was a happier and calmer person with less cycles of depression and anxiety.” Visitors to his float tanks often describe their experiences as restful and healing. “We have also seen young children float with various degrees of ADHD. We find they are able to experience more focus and a sense of calm that carries over for days and even weeks.” He compares a ninety-minute float to having 6 to 8 hours of sleep, and recommends anyone with stress, PTSD, chronic pain, or anyone simply looking to relax, to try a sensory deprivation tank.
Health benefits: https://www.healthline.com/health/sensory-deprivation-tank#benefits
Feynman’s exerpt: https://pastebin.com/42YhjjYg
Information on isolation tanks: https://en.wikipedia.org/wiki/Isolation_tank