Why do I only feel productive when I'm exhausted?

You judge a day by how wrecked you feel at the end of it. If you are not wrung out, some part of you whispers that you did not really work, that you coasted. Somewhere along the way you wired exhaustion to virtue and rest to failure, and now tiredness has become your only proof that the day counted. But exhaustion is not the same as value, and it never was. Some of your most useful days will leave you calm, because the work went smoothly, or you thought clearly, or you did the right things without thrashing. Measuring by tiredness rewards the wrong thing, effort spent, not good done, and it quietly punishes you for the very efficiency you should be proud of. Being drained is not an achievement. It is often just a cost. Try changing what you count. At the end of the day, instead of asking how tired you are, ask what actually got done and whether it mattered. Let that be the measure. A good day can end with energy left over. In fact, the best ones often do. You are allowed to do meaningful work and still walk away with something in the tank, and that is not cheating. That is doing it well.