Getting rid of all sensory input allows the ‘constantly-make-sure-you’re-not-dying’ part of your brain to chill out for a second, allowing the creative, relaxed part of your brain to come out and play. Without the constant pressure of analyzing the world around you, your body lowers its levels of cortisol, the main chemical component of stress. Your brain also releases elevated levels of dopamine and endorphins, the neurotransmitters of happiness.
Not having to fight gravity lets your muscles, joints, and bones take a well-deserved break. Your body suddenly has loads of extra resources, which it gets to focus on things like healing and resting. Without old-man gravity pushing you down all the time, your spine lengthens an inch, chronic pain is relieved, and your muscles get to fully rest. Unlike lying on a mattress, lying in water allows blood to flow freely all throughout your body. There’s no need to readjust your position to get comfortable.
About 40 minutes into your float your brain stops producing its normal Alpha waves and starts churning out Theta waves. These are responsible for that ‘between-waking-and-sleeping’ state, and you make them naturally every night. While it only lasts for a few sparse moments in your bed, you can achieve a prolonged Theta state in the tank, a state of consciousness that is usually only seen in children and people who have spent years practicing meditation.