Last year, Francie and Ali Nilforushan spent “hundreds of thousands” of dollars turning their formal dining room and a guest bedroom into a high-tech relaxation area in their ranch-style San Diego home. There’s a hyperbaric oxygen-therapy chamber, an infrared sauna, a steam shower and therapeutic lighting. But the centerpiece is a 7-foot-tall sensory-deprivation tank.

Here they can spend 30 minutes to an hour floating in saltwater in complete silence and darkness to achieve a meditative state.

“If...