Still, not quite. Basically, what Kurzban is saying is that that bad feeling that people attribute to "mental fatigue" is really just a residual feeling left over from the aversive-state votes of the monitoring mechanisms. It's not actually a way for your brain to try to communicate to you, at a conscious level, that you should do something different. You feeling that bad feeling is just a side-effect of that decision making process taking place (or, a decision that has already taken place). And, if I understand correctly, you'll feel that bad feeling more strongly when the votes from the monitoring mechanisms are more negative (which is why it generally feels harder to do things that are less immediately rewarding). If you are actually feeling like you need to sleep, though, I think that is a feeling that is actually not a part of this model.