That strange feeling that starts in your eyes and moves through your head when you haven't slept in 24 hours. I assume a caffeine high feels like this. I've never had one, though I drink lots of coffee. Symptoms:
1. bzzzzzzzzzzzzzzzzzzzzzzzzzzzz
2. everything is surreal and unconnected to reality, like images viewed through a thick glass pane.
3. people are talking to you, and you can hear what they saying, but relating to them is like pushing through gelatine. Your reactions are on instinct, from a subconscious rulebook you've picked up over years of human survival and etiquette. Nothing really matters.
4. And finally, an underlying layer of bzzzzzzzzzzzzzzzzzzzzzzzzzzzz.
And then, somewhere in the middle of the day, you crash. Total systems shutdown.
The only thing I can compare it to is Fever Bright.