Over three years the exercise regime took Rachel Cooke from terrible back pain to new levels of fitness. But it was a lot harder than she expected

One morning almost five years ago, I awoke from uneasy dreams and, like Gregor Samsa in Franz Kafka’s story, The Metamorphosis, found myself to be… well, not precisely an insect, but the effect was similar. Trying to get out of bed, I realised I could barely move. So excruciating was the pain in my back, my only option seemed to be to roll myself – thunk! – on to the floor.

Lying there on my stomach for a few moments, I took in the view (beneath the bed were old shoes and dust balls the size of planets) and then, screwing up my courage, I crawled on to the landing – which is where I stayed for the rest of the day, sobbing quietly and wondering how I would get to the loo; when, exactly, the NHS emergency doctor would arrive.