Sensory deprivation is new again! Renamed “flotation therapy,” the practice of closing oneself in a light- and soundproof tank is now trendy among self-actualizers who want to cultivate their theta-brain-wave activity. We sent the ever-intrepid Patricia Marx into the tank, which she describes as a sous-vide machine designed by George Foreman, used to cook human beings. Marx previously made a salad from Central Park weeds and drew blood practicing archery in her apartment. But relaxing, it turns out, is outside her comfort zone.