A few years ago, I developed a kidney stone. It started — or at least the pain started — while I was at the gym. I felt a niggling pain in my back like I’d tweeted a muscle. So, rather than risk making it worse, I packed up and left the gym.

By the time I got home, I was in agony. I’d never felt pain like it.

Fortunately, the stone passed painlessly the following day. But, I was left … more