I don’t hallucinate at any point during my float, although I do become acutely aware that I am a product of many eons of the evolutionary process of cephalization. Having lost any sense of my position in the room, or any sense of the room at all, the limits of my body are the borders of my spatial sense. The seat of my perceptions feels grossly off-center from the rest of me, my body basically one branching tendril grown out of my head, like the upward-sprouting growth from a spud stuck in the dirt. It feels extraneous like that, tacked-on, a slimy afterthought. Not to be cowering in the attic of my body, but to have an evenly distributed neural apparatus, like a starfish or a sea cucumber, is a balance I’ll never know.

I’m at Surrender to the Float, a sensory deprivation tank center in Guilford that, among other things, also offers classes on yoga and lucid dreaming. Co-founder Jeremy Spang told me that floating for 60 minutes in one of his tanks could help “recognize the nature of your mind.” But it’s difficult — bathed in darkness, virtually unhearing, naked, my heart squeezing and unsqueezing so that I can feel its labor — it’s difficult not to wish something more would happen.

I.

There is a sort of feedback loop in play. The more I think about this, the more I try to put words to it, the more I feel trapped in my lousy nugget of a central nervous system. Hopelessly skullbound. Hopelessly un-starfish. This is perhaps what Spang meant when he told me it would be best not to “chase after thoughts.” The injunction is familiar to anyone who has ever practiced meditation, but it’s not an easy one to follow. The brain, as Philip Corlett, a psychiatry professor at the medical school, tells me, uses prior experiences to understand new ones, and with virtually no identifiable sights and sounds, my thoughts are all I can latch onto. They present themselves in the parlance of what I’ve seen and understood previously: “cephalization,” for example, or “tendril,” or “attic.”

Corlett’s research focuses on how the brain’s demand for that which has been literally déjà vu — and the process by which it is applied to ongoing experience — can go wrong. Psychotic episodes, and their accompanying auditory or visual hallucinations, offer an example. Corlett described a model that suggests hallucinations result when “the brain becomes hungry for prior explanations, or to explain things in terms of its priors,” which leads it to make false inferences about the world. This can occur as a result of schizophrenia, psychedelic drug use, prolonged social isolation or sensory restriction.

Corlett, like Deepak Cyril D’Souza, another Yale psychiatrist, takes advantage of these last two phenomena to study psychotic symptoms, modeling them in healthy individuals using drugs and forms of sensory deprivation, sometimes in conjunction. Some people manifest visual or auditory hallucinations after long periods with restricted sensation alone, but with some drugs, D’Souza has observed a “synergism” between sensory deprivation’s effect and the drugs’.

Cody Krosky, an East Haven resident and a member at Surrender to the Float, described floating as a “step into a giant void of time and space.” Maybe one could say, then, I’ve been forced into a kind of verbal hallucination, leaving my starving brain no choice but to populate the void with words and images smuggled in from time and space — from the outside. But in my case, it might be more accurate just to call this process “metaphor.” Poetry makes nothing happen, Auden wrote. But in here, language might be the only thing preventing it from taking place.

II.

What I did in the most literal sense was float on my back in a shallow pool of salty water, enclosed in a small dark room, with earplugs in, for about 75 minutes. Versions of this practice have gone by the names of “perceptual isolation,” “sensory deprivation,” “floating” and “restricted environmental stimulation technique” (REST), among others. The object’s name,  stowed away in our minds when we enter the tank, seeking the void, will inevitably influence our expectations about it.

Perhaps this helps explain why people who float or study floating seem particularly invested in nomenclature. “Floating” sounds ethereal, relaxing, maybe a little hokey and New Age. “Sensory deprivation” sounds Spartan, ascetic, coldly medical. Peter Suedfeld, a professor emeritus of psychology at the University of British Columbia, coined the acronym “REST” in the 1970s and said he “detests” the term “sensory deprivation.” True deprivation of the senses, he said, would be possible only with “very serious drugs or with a scalpel.”

He was right: in the tank, I heard my heart beating and felt the blood coursing through my head. I heard the little sounds of dripping condensation and the occasional hum of the tank’s filter. I was aware of the soft water on my skin and the heat of the air in the room. At one point I blinked repeatedly, fascinated by the never-before-heard noise, like thick socks padding on hardwood.

III.

The various attempts to name the practice mimic the long arc of our trying to understand it. The history of REST brings together psychologists and psychonauts, the CIA and LSD, the Cold War and the New Age, interrogation and relaxation. All float in the same briny darkness.

Many still link sensory deprivation with interrogation and torture, but Suedfeld argues that the connection between REST and interrogation techniques results from a false conflation of two McGill University psychologists, Donald Ewen Cameron and Donald Hebb. Both worked in the midst of the murky research climate of the 1950s, when the CIA, through a variety of front organizations, funded research in hopes of developing psychological interrogation techniques. The CIA funded Cameron’s research, which had little to do with REST, but not Hebb’s, which laid the groundwork for the practice as it’s known today.

Hebb’s subjects, part of the first-ever studies of what the scientist called “perceptual isolation” in the first half of the 1950s, were physically restrained, wore translucent goggles and listened to unceasing random noise for long stretches of time—from a few days to a week. While most found the experience unpleasant and withdrew before their time was up, they were paid volunteers who were fed, could be led to the bathroom when they wished and could stop whenever they wanted.

Later in the 1950s, researchers moved away from Hebb’s parameters, which Suedfeld called more akin to “sensory overload,” and instead toward darkness and silence. Two of these investigators, John C. Lilly and Jay Shirley, eventually developed the direct progenitor of the modern tanks, wherein the subject floats on a buoyant solution of water and Epsom salts. Lilly studied dolphins and REST tanks and experimented with psychedelic drugs; he is often described with the epithet “psychonaut.”

Lilly published a book in 1977 titled “The Deep Self: Profound Relaxation and the Tank Isolation Technique,” which contributed to an increasing commercial interest in flotation REST tanks. The phenomenon waxed and then waned as the 1980s progressed. Suedfeld listed the common hypotheses about the reason for this: The market was limited, given the tanks’ association with psychedelic drugs and the CIA. Few viewed floating as anything more than a one-off adventure; the AIDs crisis frightened people away due to (unfounded) fears of infection in the tanks. A popular 1980 movie called “Altered States,” in which a scientist takes a hallucinogen, enters a REST tank and emerges as a sort of proto-human primate, surely didn’t help the cause.

Knowing all of this, it was hard not to feel at least a little nervous as I settled into the water at the outset of the experience. Floating, sensory deprivation, REST, perceptual isolation. If they and their murky connotations are all in the bath together, then I’m right there with them, buoyed by them, soaking them up. I wonder if I shouldn’t have done my research and conducted my interviews after the fact, so as to have had a cleaner slate going into the tank, fewer words to bring along. When I hit the rubber button that turns off the lights in the tank, there was only the music, a looping track of far-out sitar noodling, to connect me to the space I’d stepped into. In time that faded too, and then I was fully alone, fully adrift.

And at first I didn’t like it at all. My heart raced. I became a little paranoid. I was strangely vulnerable, after all, naked and shut in a dark box. I thought, admittedly, about getting out. But in the course of minutes, it passed, leaving almost nothing behind.

IV.

Surrender to the Float is located behind what looks like a residential property just off I-95. When I entered a couple of older women were sitting in the lobby, talking softly and drinking the free hot tea available on a countertop. The walls were painted a warm orange. There were plenty of plants and comfortable places to sit. Spang reclined at the front desk, wearing a warm smile, long hair, a beard and slippers.

The center represents the latest iteration of commercial REST — less like a lab and more like a spa. The practice is on its way to becoming a full-fledged cousin of yoga, meditation and acupuncture. Indeed, according to data from Float Tank Solutions, a group that hosts an annual Float Conference in Portland, Oregon, about 69 percent of centers they surveyed offer services aside from floating, the most common of which are massage, yoga and chiropractic.

Like mindfulness meditation, REST has begun to increase its mass appeal by embracing hard science. Suedfeld said the relationship between the commercial float centers and the professionals researching REST was once an antagonistic one; now, Suedfeld and some of his colleagues speak yearly at the Float Conference. Their research points to potential therapeutic benefits of floating. Suedfeld cites studies demonstrating that chamber REST — a dry version of flotation REST — has been shown to improve performance on memory tasks, enhance creativity and evoke pleasant memories. Flotation REST has been shown to reduce blood pressure and muscle tension, alleviate some types of insomnia and, when used in conjunction with positive visualization, improve athletic performance.

Exactly why REST does what it does hasn’t yet been pinned down. Some researchers have proposed that the benefits stem simply from deep relaxation, others from the shift in focus from external to internal processes, others from the prodigious quantities of Epsom salts that keep the water buoyant. Suedfeld has argued that during REST the part of the brain that is “logical and problem-solving” relinquishes its usual dominance, thus allowing “the nonlinear and nonverbal part of the brain” to become less suppressed. Increases in creativity and physical coordination are thus the result of a “change in the hemispheric dominance of the brain.” Others have taken a psychoanalytic tack and posited that a dip in the tank affects the unconscious. A few have argued that it resembles a return to the womb.

V.

This last speculation is at heart a metaphor, and one I can’t argue with. But if REST is like a glance back before birth, it’s also like a peek ahead to the tomb. Or maybe it’s a baptism in both: a dip in our beginning and our end, a quick duck out of the harsh middle and into a void.

Of course, as with most forms of escape, in the end one can’t help but come away with an awareness of escape’s impossibility. Towards the end of my float I begin desperately to need to use the bathroom. I wait it out, and in time the music comes back on to signal my time is up. I turn the tank’s light on, am blinded, turn it off, fumble for the door and step out with my hand over my eyes. I shower and check my phone, shocked to find that about 75 minutes have passed; I would have guessed about 40.

Things start to happen again. I shower and dress. I make small talk with Chris, another member of the Surrender to the Float team. A friend arrives to pick me up; on the way back we’ll stop at Best Buy to buy an adapter for his laptop. It’s dark out when we leave, about a quarter to six. I feel lighter, a little tingly, a little dazed. Snowflakes fall, incomprehensibly multiple, glinting against the darkness. They look, for a moment, like nothing I’ve ever seen before, like something for which I have no words.