Some of us remember having more energy in our 20s. We could work late, sleep badly, have a night out, recover quickly, and still feel capable the next day. By our 40s, that ease has often gone. Fatigue feels harder to shake. It's tempting to assume this is simply the ageing process – a one‑way decline. The truth is that the 40s are often the most exhausting decade, not because we are old, but because several small biological changes converge at exactly the same time that life's demands often