Floating in a float pod/tank is essentially taking the perfect therapeutic bath. Pods and tanks vary in size, but the typical pod/tank is almost 8' long and almost 5' wide. Air is allowed to freely flow in and out, and the lid never locks or latches. You have full control of your environment, sit up, open and close the lid, etc.
It holds about 11-12" of water, which is saturated with over 1000 pounds of Epsom Salts (magnesium sulfates). This creates a solution more buoyant than the Dead Sea, and you float on your back, the body is mostly in the water, your face and chest is out of the water.
The water itself is kept at the average skin temperature (94.5°F - 95°F), which allows you to lose track of your body. Inside the pod is quiet and when you turn off the light, completely dark.
No gravity, no touch, no sound, and no sight.
The buoyancy puts your body into what is essentially a zero-gravity environment: your muscles and bones get to relax, your joints and spine decompress, and the strain on your circulatory system is greatly reduced. It’s basically like your entire body breathing a sigh of relief.
With no external stimuli coming in, your system stops worrying about all the background tasks that usually keep it occupied—mostly related to not dying. Your fight-or-flight response gets a chance to kick back and stop bossing your brain around, lowering your production of adrenaline and cortisol. Instead, studies show signs that your dopamine and endorphin levels rise, giving you a natural mood high which often lasts for days.
Floating helps to release deep muscular tension, this starts a chain reaction that spreads through the body to every organ, tissue and cell. Blood pressure, heart rate, muscle tension and oxygen consumption (cell metabolism) are reduced to healthy levels. Harmful stress related hormones such as cortisol are reduced in the blood stream, enhancing emotional well being. The level of T-cells rises in the blood stream, strengthening the immune system. The brain releases a large amount of endorphins as it relaxes deeply into the theta state, relieving fatigue and chronic pain.
Restricted Environmental Stimulation Therapy affects us in another notable way; as our brains become stimuli starved, their reaction is to start creating their own stimuli. While the state of relaxation may be deep and profound, the individual’s brain stays dreamily alert. The brain gradually shifts from its usual waking beta state to generate deep alpha, theta or even delta waves, the state-of-mind where Buddhist monks try to reach through hours of meditation and years of training. You can achieve this in a matter of minutes just by lying back into the silky warm sea of bliss that is the floatation experience!
Here is a link to the Float Nation documentary on YouTube which is a great introductory film on floating.