I think what you eat has a huge bearing on that "feeling" - especially sugar. Lack of hydration also an utter killer. I don't find greasy food as much of an issue cos it usually keeps the hunger at bay and lets me sleep. Unless I've had a Dominos or giant kebab. Then it weighs me down.
Sleep is one thing I take really seriously. I just don't get how people stay up and mentally engaged til like midnight and then get up at 7AM. That hour to wind down and the inevitable waking up in middle of the night means you'd be really lucky to get 6. I have to give myself time for 9 and hope I get 7. 8 practically never seems to happen.
As for it feeling like a hangover. There's no doubt it's an unpleasant feeling but the kind of hangovers I was getting were way more severe than feeling a bit off from lack of sleep.