GP Alistair Sutcliffe suspected he was having a brain haemorrhage just as he climbed into a bath last year. Struck by an odd, fast-moving spasm in his lower neck, the GP felt the pain move to his head and disturb his balance. When he moved his head there was a deep, nauseating pain.

Showing incredible self-control, the doctor, from Whitby, north Yorkshire, managed to crawl downstairs and phone his wife, Clare, a surgeon, to ask her to organise an ambulance. "I knew that if I phoned myself I wouldn't get through the 38 questions that they have to ask," he says. "And I knew I had to stay calm as if I got all excited, my blood pressure would go up and that could kill me." He recalls that at that moment: "I thought I was going to die."

Sutcliffe, 46, was suffering from a subarachnoid haemorrhage, which although uncommon, can kill up to 50% of sufferers and often affects the young, fit and healthy. It can be caused by bulges in the blood vessel that leak and burst, malformations in blood vessels or can just be truly spontaneous. In Sutcliffe's case there was no obvious cause – although two weeks before he had tripped over one of his two border collies and banged his head. He suspects this may have been linked to his problems.

The GP was taken to Scarborough hospital, before being transferred to a specialist centre at Hull. Drifting in and out of consciousness, he struggled through recurring dreams and at one point awoke to find he had temporarily lost his sight. But he knew that the biggest risk he faced was an increased swelling in the brain that can result in "coning", where the brain stem sinks into the spinal cord, resulting in death.

Incredibly, what saved him was his very dangerous hobby – mountain climbing. Three years previously, in 2007, Sutcliffe completed the seven summits – the highest mountains in each of the world's continents. He risked death on several occasions: while climbing Aconcagua in South America, for instance, his group was confronted by two bandits on horseback, who demanded money and threatened them with a knife (they were saved when one of this fellow climbers produced a bigger knife from his waistband). On Everest his team were saved from an ice fall that killed three sherpas only because they had been delayed leaving their camp.

Yet, remarkably, his experience in summiting peaks could have ultimately protected him. A brain scan revealed that a "foetal" artery on the left side of his brain, which carries blood with oxygen to the brain in babies before they are born, was working – an unusual scenario occurring in only around 20% of adults. This artery usually becomes redundant and closes down in childhood. But it seems all the high-altitude climbing Sutcliffe had done, which meant spending time at low-oxygen levels, had put sufficient stress on his brain for this circulation to reopen – which provided an extra supply of oxygen to compensate for the vessel that was haemorrhaging. He says it was likely that this protected his brain from further damage – and probably saved his life.

Sutcliffe, who is also a keen runner, was determined to continue his climbing, and while still in hospital he worked out a recovery plan where he would walk one mile on a treadmill one day, two the next, and so on. But the first few months of his recovery were a testing time for him and Clare, who have been married for 15 years. Sutcliffe's headaches were so violent that the sound of the telephone or the dog barking could lead to three or four hours of vomiting. "It was like having meningitis every time." Clare says he was permanently irritable and she was reluctant to leave him in the house on his own when she returned to work so his father and her mother took turns to stay.

Sutcliffe's headaches worsened at night, causing tiredness. His concentration remained poor and he lost six months of his memory. In an effort to recall them again he wrote about his mountaineering, and looked at pictures of the peaks he had conquered. He began to feel the fog lifting, and the result was a book, published this month called The Hardest Climb.

Despite his difficult recovery, Sutcliffe is still as energetic as ever, running the London marathon – his 50th – this year. Ten minutes before the race began, he managed to break his rib, but still finished in four hours 43 minutes.