I partook of the waterbed phenomenon for about a minute back in the mid-80s. I blame my best friend's parents as well as my mother - they all had one when I was growing up. I bought the bed used from an ad in the paper. (My germophobic adult self is not handling that thought very well right now). You had to run a hose through a door or window into your bedroom and then wait hours (days?) for it to fill up. Then, you had to wait for the water to be heated - probably because hypothermia would ensue at some point during the REM-cycle if you didn't. Once it was filled up and heated, it looked and functioned like a great big water bottle that you somehow tucked sheets into and slept on. It felt pretty amazing - just like floating on water, but without getting yourself wet. Thinking back on it now though, it seems gauche.
As a fully upright, posture-purposeful yoga instructor, I look back on that waterbed-ownership time and wonder how well they functioned in providing proper spinal support. I also know how wonderful it would be to be able to lie on one again and feel my body move on the initial wave of impact, gradually settling down to a light ripple, and then - stillness. Except that you could never be completely still unless you held your breath. And that was a fun game, too. However, as a yoga teacher I teach my students that the only time you hold your breath outside of advanced pranayama (breathing techniques involving the retention of breath) is when you are underwater. That's the only instance. Breathing is something we are time and time again paying attention to, fine-tuning, recreating, expanding, and meditating on. We are constantly practicing the act of respiration.
On a trip to Italy five years ago, one of the first things I did was don my bathing suit, throw my towel down on the sand, and submerge myself in the Ligurian Sea at the base of Cinque Terre. I flipped right over onto my back and simply floated there in bliss while looking up at the blue skies of Tuscany. I highly recommend a good non-Atlantic Ocean-float to help relieve jet lag. Even though I've been a two-mile-a-week lap swimmer since the early 90s, I'm atypical because I will slow down enough to enjoy a good float. It's like the atypical runner who will actually take the occasional walk through the neighborhood or a park. It's a bit rare.
Floating in the water is a great sensation not only to feel the direct bodily defiance of gravity, but for the immediate awareness it gives to the sensation of breathing. Breath awareness is a major tool in the toolbox of yoga and meditation. While ambling about in our daily lives, we are mostly unaware of our breathing unless we sneeze, hiccup, cough, or have sinus congestion. Even if we are somewhat aware of our breathing, it's mostly in the chest area of the body. To completely connect with and optimize your breathing holds two requirements: 1) you have to get still and 2) you have to modify it. The modification requires a lengthening of the exhalation - more air out. If you put the effort and emphasis on the exhalation, more oxygen will automatically come into the lungs because you have just made more room for it to exist in that space. So, it's not about trying to suck in more oxygen. You have to create space first, and that requires the effort of getting more stale air (carbon dioxide) out of your lungs. This process of optimizing the breath is sometimes called "belly breathing," "diaphragmatic breathing," or "three-part breathing."
If you don't have access to a pool, a waterbed or the Mediterranean Sea but do have a bathtub, try lying back into the water and float. As you take a deep breath, you will feel yourself rise up out of the water through your chest and ribs. As you exhale, you will sink back down. The more effort you make on the exhalation, the more rise and fall movement you will get. I find this exercise soothing. It's also an interesting sensation to remain in this supine position while you drain the tub. The feeling of receding water against your skin is a caressing sensation of "wet gravity" in action. If you are near the seaside, lying on the beach right in the surf would be a hyper-version of the same sensation.
Blessings & Comfort,