Pleased to find this topic here!
I made this experience some years ago here in Hamburg. Went to a spa where they offered floatation. I booked 90 minutes. Though it was not a tank but a dark and quiet room it was quite a journey! The water - very very salty - was carrying me and after two or three minutes in getting used to this strange new environment I totally got lost. I didn't realize time was over. I thought I spent only twenty minutes or so. I cannot remember thinking. That was the most impressive thing about that. My body felt light and after a while I even didn't feel to have a body. It was like floating in space.
After getting out I felt warm and heavy and relaxed. Though very very strange. The outside world seemed to be alien. I walked home and it was like being new born.
Actually: I cannot describe it in words.
You have to try yourself.
What do I normally for relaxation?
I would say: Sleeping.
And then: Writing, Painting.
But actually this is a really difficult question.
Meditating? I cannot give insights because I haven't made it so far. Trying to meditate makes me restless. To much itching, mentally and bodily.
I would like to master it, one day.