From wiki:
A therapeutic session in a flotation tank typically lasts an hour. For the first forty minutes, it is reportedly possible to experience itching in various parts of the body (a phenomenon also reported to be common during the early stages of meditation). The last twenty minutes often end with a transition from beta or alpha brainwaves to theta, which typically occurs briefly before sleep and again at waking. In a float tank, the theta state can last for several minutes without the subject losing consciousness. Many use the extended theta state as a tool for enhanced creativity and problem solving or for superlearning. The more often the tank is used the longer the theta period becomes.[citation needed]
Spas sometimes provide commercial float tanks for use in relaxation. Flotation therapy has been academically studied in the USA and in Sweden with published results showing reduction of both pain and stress.[6] The relaxed state also involves lowered blood pressure and maximal blood flow.
Floating can be passive or active, depending on the purpose. For relaxation, one simply floats and 'clears the mind.' Active floating has many different techniques. One may perform meditation, mantras, self-hypnosis, utilize educational programs, etc. The idea of active floating is that, when the body is relaxed, the mind becomes highly suggestible and any action taken during these states will enter the information into the sub-conscious. Flotation therapy may be used to complement other body work and healing methods.