A Midnight Snack is when you're woken up, from a dead sleep, at any time between 12 am and Sun-up (it has to still be dark out) with terrible diarrhea caused by the last meal you ate before going to bed.
If you are woken up with Shit Cramps, a Midnight Snack is almost certain to immediately follow.
Bro, I ate WAY too much Chinese food. I'm definitely gonna wake up for a midnight snack tonight