I woke in the night so thirsty that my throat was on fire. Stumbling out of bed, I felt like the little mermaid in Hans Christian Andersen’s Fairy tales — as though I were walking on knives. I was only 42, but I felt crippled as I stumbled to the kitchen just across the hall. I grabbed a mug from the rack and filled it with water from the tap. I took a swig, swallowed… and poured the rest away. It was disgusting, so full of chemicals I couldn’t bear to drink it. I resorted to orange juice from the carton in the fridge. I went back to bed and lay there awake, wondering, not for the first time, what could be the matter. Why was I always thirsty? Why couldn’t I drink ordinary water? Was it me?