My anecdote: a friend of mine gave me a ticket for a float tank in London for free. Decided to try.
As others mention in this thread, it was not completely depriving of stimuli, but close enough. The air felt a bit colder than the water, so I definitely felt where one ends and the other begins. It was a 60 mins session, first 10-15 mins with relaxing music.
What was immediately noticeable to me is that I initially had incredible back pain. I realized this was just tight muscles. After some 20mins this went away and I actually felt like after a massage. Very interesting and I was almost disorientingly calm.
On out of body experiences and other magic: At around 45 mins I had slight hallucinations. A weird colorful line appeared on the horizon and I started hearing some of the best drum and bass I have ever heard (was not an existing song). Probably a flashback from my youth when I was in the scene.
All in all very interesting and I thought about buying a float tank at home (they cost 10-15k-ish). I was renting at the time however so it was not an option otherwise I would have definitely done it. It' on par or better than a massage for me when it comes to the aftereffects. The process itself is less enjoyable though than a massage.
Edit: one of the commenters asked about a bad experience.
I was actually fairly scared to try it, although I have relatively extensive experience with meditation at the time I was suffering from pretty bad anxiety and I was afraid to both meditate or try float tanks in case it makes it worse. I can say it provided a short term (hours to days) noticeable calm, so it definitely did not make it worse. YMMV