It actually surprises me when I talk about this with my friends...

I'm surprised with their reaction, too, because Lem's Pilot Pirx stories used to be a required reading at schools, and even without that it's a sci-fi classic. One of my favourite moments in that book was the test of astronauts undergone by the titular character. It was exactly what you described: floating on water and sensory deprivation. All right, maybe there were some differences since it was supposed to test the psychological resilience of the astronaut (they were required to avoid a slightest movement for as long as possible) and the test subjects wore a plaster cast of their face and ears, with a snorkel used for breathing. Sure, those scientists treated the "sensory deprivation" part seriously... Did you need to wear something like that, too?

Anyways, thanks for the post. I was fascinated with Pilot Pirx's test as a kid and sometimes imagined undergoing it myself. Now, so many years later, a random (OK, maybe not so random) post on Hive tells me that it's actually possible in my country and I don't need to join the NASA. Imma search for any floating services in Kraków or nearby, thanks again for the inspiration.