I'm running my hands through silky white sand, letting it fall through my fingers. I pick up and admire a polished white shell, then a piece of bark bleached by the sun. No, I'm not relaxing on a beach, I'm trying out the latest trend for stressed and troubled minds: sandplay.
"Sand," says Aya Husni Bey, a London-based "creative counsellor" and advocate of the all-round benefits of adult play, "is one of the purest known substances, and an ideal medium for reconnecting to our childhood.
"Most people have had contact with sand as children. Handling it can help us go back to a childlike way of feeling, a free-flowing way of being in the moment," she says.
The sand tray is only one of the "toys" on offer to adults here in Gazelli House, a swish wellness centre near London's Belgravia. With its buckets of water, brushes and painting sets, vividly coloured storybooks and boxes of charcoal and chalk, this space resembles more a busy nursery than a treatment room: the only thing missing is Play-Doh.
"Play," says Husni Bey, a certified "therapeutic play practitioner" who has worked for the UN in the Middle East and North Africa, "is crucial for alleviating stress and adults neglect it at their peril." Creative play, she believes, can help connect us with the subconscious, free emotional blockages and develop our confidence, optimism, self-worth and personal growth.
All qualities I am in dire need of: I'm in the agonising process of selling the family home and am suffering from tension headaches and sleepless nights. But being creative with crayons or clay has never really appealed: I'm too analytical, too controlling, not New Agey enough to "let go".
I'm also pretty cynical about the infantilising commercial trend towards playfulness, as evidenced by the recent colouring book craze, the obsession with animal onesies, adult ball pools and soft play nightclubs. Only yesterday an adult bouncy castle opened for three days on London's South Bank in the latest example of this bizarre type of regression.
Meanwhile, young adults are drinking less and taking fewer drugs - the proportion who are teetotal increased by 40 per cent between 2005 and 2013. Instead we get excited about cupcakes, and baking has seen a dramatic spike in popularity. Like other activities we might associate with our childhoods, these things are safe, inoffensive and carry a kind of nostalgic charm.
All of which suggests a hankering for more innocent times. For don't sand trays and bouncy castles give us, above all, a means of escape from the anxieties and difficulties of adult life? The adults at Bouncingham Castle, as the new adult bouncy castle has been dubbed, seem to think so. Here, office workers on their lunch break are among the big kids gleefully bouncing away their cares.
"My 11-year-old daughter would be incredibly jealous," says Lisa, an insurance company worker in her 40s waiting in the queue for the jelly-themed attraction. "But why shouldn't we have some fun too? Why shouldn't adults be allowed to act like children once in a while?"
Indeed, many of the bouncers believe facilities such as these should be set up permanently. "If you could pop out for a cathartic bound around after a bad morning at the office, or bounce away your Monday blues, wouldn't everyone be happier?" says Lee Simpson, a retired postal worker.
It's not the first attempt to recapture the lost innocence of childhood. In the first half of the 20th century, the Surrealists saw play as a way of reconnecting with the subconscious. Andre Breton wrote in the First Manifesto of Surrealism: "Children set off each day without a worry in the world." The difference is, instead of tapping into this idea to create art, we are now using it to alleviate stress.
Nonetheless, when my creative counsellor produces a bright blue plastic sand tray and tells me I have 25 minutes to do what I like, I am sceptical, predicting boredom will soon set in. Sitting on the floor, I obsessively try to scrape every last particle of dry sand into a neat mound. I stick a light bulb on top of my half collapsing mountain, then feel silly and remove it. I feel irritated by my inability to tidy up the sand, annoyed at the whole procedure. But after a while I stop trying to build something, to achieve an end result, and simply play with the sand. Pulling it, pushing it, sprinkling it, digging into it - just what kids do. I get lost in play, to the point where I (almost) stop thinking.
Trying to "tidy up" the sand tray is quite common, apparently; others use the figurines and other objects provided to play out past traumas.
I also tried out the watercolours, to produce a surprisingly bold painting of which I felt rather proud, just like a child. Could it have significance - a journey from the dark (the midnight blue paint I daubed on) into the light (the yellow patch I created in a corner)? But I felt sceptical whether it meant anything at all.
My last playtime task was to write a poem or story - or even just spontaneously set down words as they occurred. Feeling self-conscious, I managed something about escaping from a dark forest, crawling through the undergrowth, getting caught in brambles, emerging into sunlight.
My conclusion? I was pleasantly surprised at my ability, after an uneasy start, to lose myself in the sand and the painting. I certainly wasn't convinced it meant anything deeper. And couldn't one just as easily indulge in play at home rather than pay up to 70 pounds (NZ$146) an hour for the privilege?
Husni Bey thinks otherwise. "When we play, we drop a lot of survival mechanisms we need in the outside world and tap into the spontaneous part of ourselves," she says. "But this can also make us feel vulnerable. The counsellor provides a safe space to help you explore that childhood self."
Certainly, many experts affirm the transformative power of creative play, which is sometimes used in psychotherapy. Dr Stuart Brown, a US psychiatrist from California and a pioneer in research on play, says keeping up the habit in adulthood can make us smarter. "Of all animal species, humans are the biggest players of all. We are built to play and built through play. Most obviously, it is intensely pleasurable. It energises and enlivens us. It eases our burdens."
After my session I felt tired and even a little weepy - a bit like a toddler who has spent the morning messing about in the playroom and is ready for a nap.