The first heatwave of the year always feels like a genuine cause for celebration, that long-awaited reprieve from months of dull grey skies and near-daily showers. But after a few joyous pints in the sun, a new problem sets in: how to sleep in hot weather, through all that sweat. “People’s core body temperature will be different from one person to the next,” says Dr Zoe Gotts from The London Sleep Centre.