I suppose this isn’t news to anyone, but as soon as I started ensuring I hit my fitness targets each day, the quality of thought, action, sleep quality, and achievement across the board improved.
It was just a short swim three days ago, and then very simple bodyweight exercises — jumping jacks, air squats, pushups, bicycle situps — but apparently it’s enough to trigger that totality-of-whatever-it-is that makes fitness give its huge boosts.
The Lights Spreadsheet is nice in that, when things are starting to get shaky, it’s possible to precisely nail where, and look for correlations and causation. No fitness = a big problem.