So last night I had my first floatation experience.
Initially it felt really funny, being pushed to the surface as if being filled with air. But I then immediately became aware of how tense the muscles in my neck and shoulders are, and I clearly felt all other tensions and pain in my body. The floating provided sort of a three dimensional diagnosis of my body.
Throughout the session I sometimes turned the music on, then off again, and had to get used to (softly) bumping against the sides of the tank, and pushing the buttons for (quite limited and noisy) ventilation etc. But since the session took an hour, I got plenty of time to become still, which also reduced the bumping.
I had inhaled some weed half an hour before, which had the negative side effect of closing my right nostril, which made it necessary for me to breathe through my mouth. After forty minutes or so the nostril opened again, and I could spend the final part in complete relaxation.
The session wasn't psychedelic. There were neither visual nor significantly psychological effects. It seems I was mainly confronted, as I usually am during trips, with the fact that my muscular system is way too tense. Floating certainly took some tension away, because during the second half hour it was much less noticeable.
Now as far as tripping in a floatation tank is concerned, I think it would definitely be possible, pleasing and useful, even in this particular public floatation center (you can bring your own music!). But you need to have a (couple of) sober sessions first, to get used to the buttons for light, music and ventilation (or help from the operator), the different physical sensations, the relative lack of oxygen, finding the best posture(s) to float, and most of all not getting the extremely salty water in your eyes.
I paid for three sessions, so I've got two more to go.