You're staying up late for some reason.
You've been studying/working past 8 'o clock. You've had dinner only after that.
You have more coffee in your system than Brazil, and now, it's 4 o'clock. AM.
You should go sleep. And then there's this one site, or one really cool person you start talking to.
And the coffee wears off.
Now what? Do you keep yourself awake? You know you should go sleep, your body is telling you to go sleep, and your friend might also tell you to go sleep. They might even tell you so, on the hour, every hour, and then tell you to wake up, because you've got a test/appointment the next day.
I'm not asking whether or not you know that feeling (because you do ^^).
I'm just stating something here.