Your hypothalamus regulates body temperature. It also partially regulates sleep and appetite. A lot of research has been done on sleep deprivation, because military funding is vast and soldiers regularly experience it. In every sleep deprivation paper I've read that measured body temperature, it caused a drop. It also causes people to shove everything that is edible into their mouths.
I'm going to preface this by saying that I think evolutionary psychology is generally stupid, but maybe almost all of your ancestors evolved in an environment where they didn't have the option of remaining alert after the sun set. Don't mess with your sleep cycle. This is coming from someone who used to regularly pull all-nighters in graduate school and hasn't in almost a decade.
