There is a particular kind of tiredness that sleep doesn't fix. You know it well. You wake after a full night and still feel it, a low hum of tension sitting somewhere behind the eyes, a restlessness that has nothing to do with physical fatigue, a sense that you are perpetually slightly behind yourself. You are not ill. You are not even especially stressed, by the standards of your life. You are simply running on a nervous system that has forgotten what it feels like to be at rest.

Most people who step into a sauna for the first time know roughly what to expect: it's going to be hot, they're going to sweat, and they'll probably feel pretty good afterwards. What they don't expect is quite how much is happening beneath the surface and how profound those changes actually are.

When most people try to build a wellness habit, they focus on the outcome: I want to feel less stressed. I want to sleep better. I want to be healthier. These are fine goals, but they're located in the future and the future is abstract. It doesn't pull you out of bed on a cold Tuesday morning.

We talk about stress as though it's just a feeling. A bad week at work, a difficult conversation, a too-long to-do list. But beneath the surface, chronic stress is doing something far more serious; it's quietly shortening your life.

Poor sleep is one of the most common complaints of modern life. Around one in three adults in the UK report regularly not getting enough of it. We lie awake at night with a restless mind, wake in the small hours unable to settle, or drag ourselves through the day on four or five broken hours, relying on caffeine to paper over the cracks.