Induction of altered states of consciousness during Floatation-REST is associated with the dissolution of body boundaries and the distortion of subjective time

Floatation-REST (Reduced Environmental Stimulation Therapy) is a sensory isolation technique where subjects are immersed in an environment without sound or light while they float in thermoneutral water that is supersaturated with Epsom salt. Here we investigated the relationship between altered states of consciousness (ASC) and its association with the affective changes induced by Floatation-REST. Using a within-subject crossover design, 50 subjects were randomized to either 60 minutes of Floatation-REST or 60 minutes of Bed-REST. ASC was assessed using the Phenomenology of Consciousness Inventory (PCI), the Perceived Body Boundaries Scale (PBBS), and visual analogue scales targeting time perception. Emotional changes were assessed both before and after each REST session. Compared to Bed-REST, Floatation-REST significantly reduced perceived body boundaries and distorted time perception. Two subscales of the PCI showed stronger ASC during Floatation-REST versus Bed-REST. Subjects felt more relaxed, less anxious, and less tired after Floatation-REST. Dissolution of body boundaries mediates anxiety reduction, revealing a novel anxiolytic mechanism.