These are some cool data. I am currently gathering data on a small sample of emergency physicians to determine the relationship between sleep, overnight shift work and mood, among other things. We have not analyzed those data yet, but in a larger sample (from a commercial source), it appears that sleep duration has a prominent effect on mood.
My question: is there an evolutionary explanation for the relationship between sleep duration and mood? Is it plausible that a bad mood from poor sleep is adaptive? Why?