The sound of the waves is not so different from the traffic of the city. But as soon as you lift your face and taste the fresh tang of salt on the air, you will mark how this sky is as different, fickle and changeable as all you have left behind. Then, if you listen, you will hear the laughing gulls. And beyond that, heading off in a low V-shape, the haunting call of the geese.

I have lived in the Hebrides for more than 16 years – the first years with my husband, and for the past decade with my dog, Maude, alone. I had been dreaming of staring out at a raw, open horizon for years – ever since I found an old map of Scotland and pinned it up in the hallway in my London flat. It was positioned across the full length of a narrow wall where I always saw it as I was passing, at an angle where your eyes fell into that empty space between giant masses of land. It is always during that notion of transit, of passing from one space to another, that your heart opens and all of your dreaming begins. I would press my nose to that thick paper, inhaling its musty scent, as my finger traced the ragged coastline of the fractured islets and islands. In those moments, as my eyes closed, the traffic, shouts from the street, neighbours slamming doors, would evaporate into the hurl of fresh spindrift, the thick, curling crests of the breakers drenching the salt-stung air, the gulls tearing the skies apart with an aching, screaming call.

I had loved my early years in London. I lived in Notting Hill, in a flat with an iron gate leading out on to communal garden. It was a sanctuary in the heart of the city, with a buzzing, cosmopolitan local community on tap. I was there years before the film came out, when you bought your vegetables in a brown paper bag with cash, knew all the street vendors, got your cigarettes from the cashier at the toy shop on the corner of Kensington Park Road. It was a time of hope and dreaming of your beautiful life, and Britpop singing the world real again.

But in London, neighbourhoods are transient and can shift as quickly as the low skies gusting overhead. Suddenly, there was a disconcerting invisibility to the formerly gregarious community and a disheartening, unsettling and desolate feeling that permeated the streets. People started walking more quickly, heads bowed, barely meeting your eyes. Humanity is a vulnerable, vigilant thing. Our building was spray-painted with graffiti, windows were broken, the police were called. One day, arriving home, I screamed as I walked into the back garden. The plants were torn apart, some that were flowering had been uprooted. I fought tears as I looked into the pond. Cans of paint had been poured over the wall, the containers left floating in the water. Hidden in the reeds were the faded, bloated corpses of our beautiful, bright little fish. Something died in me that day.

A neighbour was mugged, then another knocked to the ground. I stopped walking around the neighbourhood. Those weeks were a tense, nail-biting time when everything became dark and feral. Worn down by months of this, I started waking in the night, feeling breathless, my heart thudding. Stress is invisible; subtle and insidious, it builds up over time. Anxiety is like a smouldering fire. All it takes is a scream, a moment of fear, to whip those flickering embers into burning flames.

It was the fall of silence that struck me. It had a porous feel to it, as if the sky had been spilled into it until there was room for little else. No raised voices, no bricks through the window. No rattling of sticks on a metal grille, or buses thundering past. Inside, there was a stillness like cool, clear water. And I knew that it was this quiet that I had been seeking for so long. It did not matter that the cottage we had moved our lives into had no water, electricity, outside drains or paint on its walls. It did not matter that there was no heating or insulation. Nor that it was as freezing cold inside as it was outside, with just a single stone grate in one end wall. It did not matter that it was unloved and had not been lived in for five years.

I will never forget the day I travelled to start my life on the island. Arriving alone, as a stranger, was one of those unnerving twists of fate that only holds a deeper resonance in later years. I like to think it was my first test of facing my fears and putting my trust in the unknown. Looking back, I had no idea that those early years would only be the start of a fiercer, wilder, intensely difficult period that would tax my courage, resilience and endurance to breaking point and beyond. Growth is not always easy, and sometimes a new seed has to be encouraged, even forced, to grow.

The island is barely 12 miles long, its narrow girth tightening to half a mile, with close to 140 residents, another 10 or so renting temporarily. I had not planned to be here alone. We arrived as a couple and at first we were happy. When my husband left, the challenges began. I was grief-stricken and struggling to cope. My father had only recently died and my mother had been diagnosed with a terminal illness. I was still shattered by devastating loss after years of infertility, up to my neck in crippling debt and unable to work, struggling to function. My confidence was drained; I had broken both of my hands in two separate accidents, and simple tasks became overwhelmingly difficult. I felt helpless. Then my best friend – a woman I had met on the island – was killed in a car crash.

Grief is like soil. It is heavy and clings to your skin when you come up for air. Sometimes even after you have brushed it off it is suddenly there again, miring you in something dead and weighted and dark.

For a few years, solitude became all my life. When I lived in London, solitude was synonymous with relaxation. It meant a pause or vital decompression, a moment of balancing, a slow drawing of breath – an experience to be savoured. It was never so internal as to be a state or frame of mind. I looked forward to it – time set aside to allow something restricted inside to free itself. On the island, my experience of isolation was frightening because it so quickly normalised – a clear, cold wind of solitude that I used to love now wrapped around me, a constant presence. I began to notice I was often shivering, how the days felt cold. Isolation is a process of self-harming. You do not wish to go there, but over time it feels a safe place to be. It is addictive.

I have always been sociable and, in London, was used to being surrounded by company. I knew something was wrong when I felt unable to connect with others on the island. I kept trying to reach out, but it was as if some inner inhibition was blocking me, so each encounter hurt, like a bruising collision. Authentic connection is made more difficult when you are living alone, at a distance from close friends and family. I found myself searching others’ eyes like a moth seeking a light – but my eyes were always too wanting or hopeful. Over time, those collisions felt increasingly sharp, abrasive.

When I was most isolated, I was also coping with an acute yet chronic respiratory illness and my immune system collapsed. Each intake of breath felt like inhaling tiny shards of glass. One winter night, I forced myself out of the house. I stood alone, wrapped in blankets, shivering in the darkness. It was such a comfort to look up and feel that great breathing night sky around me, eyes wide, gazing into a dark glittering universe of stars. It helped me to take a breath, force myself to stretch out, to release that suffocating inhibition. That night, I lifted my arms and asked for help. I was aware of feeling some mysterious reciprocity of kindness. Something inexpressible in the immense darkness answered me.

Now I embrace solitude. For the past four years, at dawn, I have run across the hills to the sea. It was the sea that helped me break that cold silence inside. Each day I throw lost hours into the water. It renews my strength, fires resilience inside and gives me a sense of gratitude for my warm breath and beating heart. I never used to like cold water, yet here I have grown to love its shocking, icy embrace. Every day, whatever the weather, I rise early and head for the shore. I have not missed a day, regardless of storms and punishing Hebridean conditions. I have swum in snow, in freezing rain with thick ice particles obscuring visibility, in crisp sunshine and in dense mist, and once with the wind chill dipping to -16C and the solid, crackling edges of the sea freezing.

Standing on the shoreline as the waves come barrelling towards you helps you to step into all you normally draw back from. Cold water swimming takes you beyond resistance. It invites you to ask, “What else do you fear?” It forces you to tackle all in your life that has a stronger undertow. In the water there is no place for fear. I used to tell myself, “Soon I will stop.” Eventually, I realised I didn’t want to. It gets me up to set firm boundaries. It teaches stamina, courage, inner resilience and buoyancy. Sometimes you think you have nothing left to give, and then it asks for more, so you give more of yourself than you ever imagined was possible. If I can stand bare-skinned in the freezing cold, hurl myself into the waves and keep swimming, then I am winning.

Solitude helps you to redraw your own parameters, but its navigation takes skill and practice. Immersed in nature, you learn to look to the tides, winds, weather, currents, and raw elements more closely. That knowledge becomes instinctive. When I am alone, I am more focused and attuned to the particular nuances and subtleties in the natural world around me. Life is simplified. You feel your own humanity, physicality and interconnectedness acutely.

These days, life runs calmly. I have dear friends and close community, yet I still value and actively make space for my own solitude. I still do not have family, kin, children, so I have learned to fill that space with different, other lives. Now I understand how isolation and often the most shattering experiences in life are so important. The profound depth of our suffering holds all kinds of hidden truths. Nature is regenerative. Everything has to break down in order to renew.

Each morning, as I wake to the dawn sky and the sun rising over the mountains, the sound of the wind and weather is a familiar, loved presence. I always sleep with my window open. If I listen, I hear the buzzards and a great silence of mountains beyond. It is quiet when I go downstairs. There is always a quality of stillness that is only felt in an old house. In winter the power still goes off and so the early mornings start with candlelight. I rarely eat alone. Wild birds often fly in the open windows. They sit perched on a gnarled hazel twig that swings tied to a branch I use as a curtain rail. We sit and watch each other as I talk to Maude, pressed close against my legs.

When you immerse yourself deeply into nature, exposing yourself to discomfort and risk, you recalibrate more sensitively to unseen patterns and rhythms. You feel your own pulse and breath instilled with a peace and calmness. The rugged landscape becomes hewn differently, takes on more intimate contours. Immersed daily in the sea, swimming in all weathers, it is interesting how other aspects of your life start adjusting to this routine. Tasks are organised differently, more closely aligned to the bigger cycles of sun, moon and tides and seasonal shifts. Some call this biodynamic living, and it makes sense. It connects the unique solitude of every animate or inanimate sentience, and connects it to an expansive, interconnected universe.

That realisation came to me one early dawn. It was freezing, the depths of winter. I stripped off and dived into the waves. Out in the channel, the wind had dropped and snow, long promised, started to fall. Then something happened that changed my life. A wilder voice called my name with love and changed me forever. Afterwards, all it takes is a breath to reconnect to the pulse and beat of the universe. Once that feeling is experienced, it is impossible ever to feel alone.

To order a copy of I Am An Island by Tamsin Calidas (Doubleday, £16.99) for £14.78, go to guardianbookshop.com