What is floatation?

A floatation tank contains 10 inches of super-saturated salt solution, creating an environment similar to the Dead Sea which enables you to float effortlessly on the surface.

The water is heated to skin temperature, so that it's virtually impossible to distinguish between parts of the body that are in contact with the water, and those that aren't, in effect "fooling" the brain into believing that the person is floating in mid-air.