You fall asleep without much trouble. Then suddenly your eyes open. You reach for the clock. 3:07 AM. The next night, it happens again. Maybe it's 2:42. Maybe 3:30. Maybe 4:00. After enough repetitions, it starts to feel strangely specific. And if you've searched online for an explanation, you've probably encountered confident answers: It's your cortisol. Your blood sugar is crashing. Your liver is waking you up. Your hormones are out of balance. The reality is less dramatic—

You went to bed at a reasonable time. You didn't run a marathon yesterday. Your schedule may be busy, but it isn't dramatically different from a few years ago. And yet by mid-afternoon, you feel as though your battery is almost empty. If this sounds familiar, you may have wondered: Why am I so tired after 40? It is tempting to blame age. Or hormones. Or a “slower metabolism.” But fatigue is not a diagnosis, and turning 40 does not create a single biological reason for low ene