I think Daniel Kahneman's System 1 (habits, unconscious) and System 2 (learning, "error correction", conscious) are physical systems, and System 2 takes a LOT more energy to run.

So, when you get tired, System 2 leans more and more on the much more energy efficient System 1. So you get behaviors that look like unrestrained habits: poor impulse control, lowered emotional regulation, etc

Edit: I wrote more about this idea if anyone is curious: https://1393.xyz/writing/alzheimers-is-the-symptom-not-the-p...