That was all the rage a few years back. There were places that an individual could rent for an hour or a day. There was no sound, no light, and often had water as in a shallow swimming pool. SOme of the users of such places reported positive outcomes.....peace, tranquility, and all that.
I have a book about the orchestration of biologic rhythms. It is about circadian clocks. More than a few volunteer research experimenters have been spelunkers. The "cave men" would isolate themselves underground for long periods of time, 100 days or more. The rhythmic wake/sleep cycles were pretty well established as being the same as ordinary above ground existence. The cave dwellers did have some spooky psychiatric quirks after the self administered, long term, isolation in a soundless, cold, dark, place.
As a matter of fact I suspect that cave people are nuts in the first place. I can harbor that belief strongly because I am very much claustrophobic. ...
One of the most upsetting experiences in my life was in an MRI machine....one of the kinds that send you into a small tube like structure and no way in hell you can get out of it unless you press the panic button that the operator/technician said would signal them to remove you from the tube and the panic. What if the operator was a fiend who liked to torture people. That MRi technician would not respond to the panic button and what if the panic button was not even functional and it was all a diabolical lie. Forty five minutes in that noisy hammering hellish tube was/is more than a fraidy cat can endure and hope to survive sane after the fact.
The one time that I did that MRI torture was an adventure in mind over wildly irrational fear. I had been in the distant past an exceptionally skilled motorcycle mechanic. While in the tube, I forced my mind to paint mental vivid pictures of a complete disassembly and reassembly of a Royal Enfield single cylinder motorcycle engine. The fear driven realism was vivid. I handled mentally and vividly manipulated every bolt and nut in that engine, piece by piece and in the proper order of disassembly and subsequent re-assembly. That was one of the most strenuous exercises of total concentration in my whole life. If only I could have concentrated that spectacularly well during my struggles with my university calculus classes. But then I was not in fear of my life in calc class.
I got out of the hell machine intact, but in the immediate aftermath it required two heavily re-inforced margaritas to calm myself down........So if there is some positive outcomes of isolation tanks, I ain't ever going to enjoy such an experience. Isolation tanks are the instruments of Lucifer himself for some of us. A cool place to be for others.