Does flotation-rest (restricted environmental stimulation technique) have an effect on sleep?

Introduction: Some therapies described within alternative and complementary medicine are advertised as sleep-promoting, including flotation-REST (Restricted Environmental Stimulation Technique). Flotation-REST induces deep relaxation through sensory isolation in a water-filled tank and is plausibly reported to mitigate insomnia problems, which have consistently been associated with stress, worry and arousal. However, the effects of flotation-REST have not been previously summarised. The aim of this systematic review was to investigate the efficacy of flotation-REST on sleep in clinical and non-clinical samples. Methods: A systematic search for studies on flotation-REST, involving at least one sleep-related variable, was conducted in the databases PubMed, Google Scholar, Web of Science and PsychINFO. Thirteen full-text articles met the inclusion criteria and were considered for eligibility. Nine were included in the current review. The methodological quality of the studies was assessed using a structured checklist, and a standard data extraction sheet was used to summarize the ratings. Results: In all included studies, flotation-REST demonstrated beneficial effects on sleep, both in clinical and nonclinical samples. In two studies, the effects were maintained 4 or 6 months post-treatment. The quality of the sleep outcome measures were, however, low in most studies, particularly regarding the participants' nightly sleep habits, self-reported sleep problems and insomnia diagnosis. Conclusions: Flotation-REST may be a promising treatment for insomnia symptoms, but more controlled studies with established sleep measures, and on populations with clinically verified insomnia, are needed.