For some reason, I stop feeling tired after I stay up too late. It's not that I'm not tired, because when I reach this point I can fall asleep almost immediately if I lay down, but if I am sitting or standing, I don't really get tired. Also, I find doing a task that doesn't require much thinking, like mindlessly playing video games, helps me wake up. It must be because my brain falls asleep while doing this, or something.