I'm wondering what exactly the neuro-chemical basis for "tiredness" is. Not tiredness in a subjective, feeling type of way, but an actually physical event or state (like low glucose) that will cause a person to be have mentally low energy. not "sleepiness", but rather mentally tired. Also interested in why this seems to happen after food consumption... what postprandial mechanism is going on? Any thoughts?

after food consumption, blood is diverted to the digestive system, leaving less for the nervous system. Hence, postprandial sleepiness.

I welcome the emergence of anorexic Politicians!!

You should always remember that nerve fibers and neural cells are tireless, even they don't know what the fatigue is! Synaptic junctions are fatiguable as a result of shotage of neurotransmitter in the cleft. When evening's coming up, our synapses work worse than they do after awakening -> glutamate has been expended, therefore the CNS is tired.