Hi Wendy,
Not a problem. It felt a little weird at first lying on the water bed thing. Back-wise I have a tendency to be tense at the base of the spine, and my bum sticks out (making me look like a duck ) so I usually like a pillow under my knees. With the water-bed my back didn't feel too happy at first, like I was sticking out my bum even more. However, the heat was blissful and I soon got used ot it. I'm a soul who has tepid showers because I overheat (hot stone massage is also too much for me) but this was just lovely. It remains at a constant temperature - can't remember what that is now.
I was a bit dubious that the therapist's hands would slide around underneath me as well as the marketing blurb boasted, but it was effortless. I was trying to take mental notes as I relaxed, and I remember the effleurage at the start was: therapist standing facing my right side; hands slide in just above glutes then glide around the hip, running up the erector spinae and around the scapula. The heat and the technique together were lovely, and after my muscles started to relax due to the heat - which obviously happens quicker than a normal massage - as she massaged me, I did wobble about, but it was like my limbs were floating , if that makes sense; they were free to move about naturally, and it was extremely calming as well as liberating. At the time I had this massage I was going through a tough time emotionally, and it was just what I needed. In fact, after a strenuous couple of days, and coupled with your thread as a reminder, I'm thinking of booking another one for Friday if my local place can fit me in.
Hope this helps, and if you have any more questions, post again and I'll reply asap. I'm generally lurking on HP somewhere a few times every day