I am a runner – and I suffer from post-traumatic stress disorder. One of the many things I think about while I'm running, and also when I'm not, is the relationship between the two.

I have always loved to run, and I have fuzzy memories of running pretty much anywhere, anytime, as a child. We would spend family holidays in north Wales, and I remember galloping into the hills, pretending to be a horse, then sitting in the grass and watching a snowstorm move up the valley. Now in my 40s, running has become far more structured, and an essential contribution to my life and ability to manage my illness. Yet I find that some people are concerned about my need for it, which always surprises me, as it seems like a positive thing to do. One doctor recently asked me if it felt like I was running away and I answered: "What does it matter? It makes me feel better."

Experiences of loss and repeated trauma from childhood resulted in an early onset of depression and severe anxiety, culminating in a complete breakdown at 27 from which I've never fully recovered. It took over 30 years of seeing multiple mental health professionals before I even had an explanation for my inability to get well (a correct diagnosis was only reached in my late30s). A good day for me is managing the walk to my son's school, greeting teachers and other parents, then perhaps doing some food shopping, without having a panic attack. On a really good day, I might have a friend round for coffee and a chat, but by and large my life is isolated – and that's OK. My wonderful husband enjoys taking the boys out, while I (for the most part) am the stay-at-home support. I have more than I ever dreamed possible.

Four years ago, my husband's work took us to the US, where our second son was born, and shortly after that a friend introduced me to trail running. I have always felt at home in the mountains, and the Appalachians are breathtakingly beautiful. At first, I couldn't manage more than a mile or two without stopping, but I nonetheless made the most incredible discovery. How to articulate this? As well as the powerful medicinal effect of being surrounded by nature, running makes life feel simple. Battling an illness such as mine is utterly debilitating all day, every day, year after year. There is no respite. Many people will know what I mean when I refer to having a dream where you are suddenly, sharply falling, causing you to wake with a jolt and a racing heart. I have this sensation many times a day while wide awake, for absolutely no visible reason – I am perpetually fearful. In addition to this, the depression (and grief) can be crippling: it slowly numbs your brain and sends your body into a state I imagine being rather like hibernation – an attempt to withdraw from the pain. Going for a run not only gets me physically moving, it also takes my thoughts out of the equation: all I have to do is keep putting one foot in front of the other and breathe.

Initially, my incentive was an 18-mile trail race up a mountain, with a total of around 5,300ft of ascent. Having been a 100-metre sprinter at school, this seemed like an impossible, if not ludicrous, goal, but it somehow represented my life. I knew a run of that magnitude was going to be physically and mentally exhausting, as well as painful, but I needed, at the very least, to survive it. It was a daunting challenge, and I was almost convinced that failure was inevitable, but I approached it by being scientific: reading, researching, asking advice and putting my trust in training. Even just getting out for a run could be next to impossible, due to my agoraphobia. Some runs would be particularly fast, with the extra injection of fear-induced adrenaline. And I had a very patient, kind partner for the weekend long runs, which I could never have done on my own.

On the day of the race, I kept my head down to avoid total panic among the crowd of runners at the start and set no time target: it was about getting to my family at the finish line and looking at the view from the top of the mountain; being, for once in my life, one of the achievers.

That was over a year ago, and we have now moved to yet another country, but I have brought the running with me, along with my race finisher's shirt. Our new home backs onto 2,000ft of rugged hill, with rocky, brutally steep trails to the summit, from where miles and miles of mountain tops stretch away to the edge of the Earth. I embrace running in all weathers: sun, heavy rain, high winds, snow and hail, always with a considerable amount of ascent. As I fight my way up the climbs, I often imagine that the hill is my illness and I am going to slowly and steadily conquer it. Yet it never feels like suffering and, once at the top of the hill, I can reach out and touch the sky. At home, I am always struggling to stay afloat, fearing I will lose the battle with my illness and fail my husband and children, but all of that slips away when I am running. It is just me and the hills and some long-distant memories, and I always come home smiling and with my head full of stillness.