I’d just completed the spectacular four-day Inca Trail hike to Machu Picchu and, drunk on nature, was feeling dangerously invincible. Fresh Peruvian air still rejuvenated my lungs and the brain fog induced by my daily smartphone addiction hadn’t yet crept back in.

The disastrous events that followed began once I turned my phone back on. Responding to a Twitter solicitation for Peru recommendations, a man I’d never met posted: “Go mountain biking down a volcano in Arequipa!”

Those eight words would change my life.

I didn’t even know what Arequipa was, and yet within an hour of the tweet I’d resolved to change all my plans and go. I waved goodbye to my hiking buddy and swapped my flight to Lima, Peru’s capital, for Arequipa, its second biggest city, noted for its striking volcanoes, valleys and adventure sports.

As I’m a lifelong adrenaline junkie, the opportunity felt irresistible. I’ve skydived, sand-dune surfed, paraglided, bungee-jumped off New Zealand’s tallest tower, been propelled from the water into the air by a jet pack and done Tough Mudder-style adventure events which included ice baths and an “electroshock therapy” obstacle of 10,000 volts.

These experiences shouldn’t be taken as braggadocio that claims: “I’m mad, me!” but more as a recognition of a lifelong problem. I had always found the pedestrian, repetitive monotony of daily life stultifying without a semi-regular thrill to remind me of my own mortality. Descending a volcano by mountain bike felt too seductive, a once-in-a-lifetime experience I couldn’t let pass.

I struggled to find a tour company that would take me as a solo rider. Three suppliers cancelled at the last minute the night before. It was almost as if the universe was telling me something bad would happen. Still, I ignored such signs and finally found a guide.

My head brushed the roof of the 4x4 as I set out with my guide and a driver for the two-hour journey up the winding Pichu Pichu volcano which dominates the city’s skyline, so tall at 4,200m that my ears popped on the ascent. As the SUV rolled over the volcano’s ancient lava-encrusted bumps, a familiar feeling returned to my gut: nervousness, excitement, the feeling of being alive.

My guide offered me four routes, increasing in order of difficulty. He tried to get me to buy the fourth – the hardest (and most expensive). I opted for the third. At the summit I geared up: knee pads, elbow pads, helmet, extra layers. Initially the descent – down a spiralling gravel path which wrapped around Pichu Pichu – was glorious. I belted Life by Des’ree as we whizzed down the winding track. Adrenaline surged through me. My guide showed me three “shortcut” off-road descents straight down from the spiral. I declined each for being too steep until it started to get awkward – I’d literally paid him to take me off road, and I was staying on road. I agreed to the fourth descent.

Suddenly the hills felt perilous; I was almost at a 90-degree angle. My singing abruptly stopped. My colon travelled to my larynx. I screamed at an emasculating pitch and surprising volume. “Well done, Mr Gary!” my guide said, laughing, as I completed a steep descent. “Remember: don’t brake on the hill.”

The bike then picked up an alarming pace. I felt panic travel through me. I resisted braking for most of the descent till it felt too dangerously fast. I saw my guide, who’d stopped ahead of me on the narrow rocky trail, rapidly nearing. Fearful I’d knock him over, I braked too hard into a skid.

Furious amounts of dry dust erupted from the hilly dirt ground in protest. My back wheel flipped up, throwing me over the handlebars. In a wallop, my entire body weight landed on my right wrist. Through the clouds of dirt, I briefly saw the outline of my bike in the air. The dust cleared enough for me to see it hurtling towards me before landing on top of me, instantly winding me. At altitude.

Arid soil filled my mouth; the first thing I did was spit. I could barely breathe. My hearing faded back in. “Mr Gary? Mr Gary, are you OK?”

I was too winded and in shock to respond. “Catch your breath, Mr Gary,” my guide said. The first word I choked out was an expletive. The first feeling was sheer embarrassment. Then disappointment. Then pain.

My guide insisted my wrist definitely wasn’t broken; he’s a former paramedic, and if it was broken, it would have swollen more, he said. He even tried getting me back on the bike, but I was in too much pain. Deflated, I asked him to radio the van-of-shame to drive me the rest of the way down the volcano. I slipped and slid down the dusty narrow trail, swearing each time I bumped my wrist.

The next day, in agony, I headed to a private clinic. My wrist was definitely broken. Broken so badly that, eight months on, my wrist still isn’t fully functional.

Looking back on that last adrenaline-fuelled ride, I feel both idiotic and philosophical, sad and cautious. I should have eased in more gently on an easier route. Cycling fast both on and off road has long been my passion, but at the age of 42 I have reluctantly conceded that my mountain-biking days are probably over. Doing the same thing and expecting different results is madness. Twenty minutes of euphoria just isn’t worth the risk of two months in a plaster cast then many more in physio.

And it’s not just mountain biking I’ve turned the page on. Gently letting go of the thrill-seeking side of myself is a reluctant metamorphosis, but one that recognises both a 36-hour rave at Berghain and a broken bone will take longer to recover from as I ease into middle-age. Each action has an equal and opposite reaction, and that reaction lengthens and intensifies, arguably from your 40s onwards. Each activity will now require a clear-headed risk assessment by speaking it through with someone less gung-ho than me. Four-day hiking with tents? Yes. Canyoning? Maybe. Free solo rockclimbing? Absolutely not. I’m currently deciding whether to ride the world’s largest zip-line system in Mexico next month. Jury’s still out. The old me would’ve already booked it.

Quitting adrenaline-seeking activities has made me take a closer look at my thrill-seeking need and what it says about me. I was recently diagnosed with ADHD by a psychiatrist. I’m still figuring out what this means for me, and how to manage it, but it contextualises my risk-taking. While it’s a popular aphorism for wellness memes and trite wall-hangings, the spontaneity of the “carpe diem” or “yolo” mindset is all well and good till you’re in a foreign hospital being told you need bone-resetting surgery costing £4,000 – and your travel insurance won’t pay. I’ve realised: sometimes living for tomorrow is healthier than living for today.

• Gary Nunn is a freelance journalist and author