I've wanted to do this since I was a kid, and finally getting to was just incredible. The most relaxing experience I've ever had. There's an adjustment period where my thoughts kept wandering, and I kept bumping into the sides of the tank, and I was freaking out going "oh god I'm not relaxing right I'm screwing it up." But then I came to rest, and the lights and the soft music drifted off to leave me in total darkness and silence, and it felt wonderful. The water is so thick with salt that it's almost more like being in a warm smoothie than in water. Eventually you can't tell where your skin ends and the water begins. I was also worried about my ADHD not letting me enjoy the full time, but when my hour was up I literally thought it had been 20 minutes.
Highly recommending this experience-- I had never felt so relaxed, physically or mentally, and it stayed with me all day.