It's a comedown. Your serotonin and dopamine levels are depleted. It's how you feel after taking cocaine/ecstasy.
The worst is a combination of a fun night, a huge embarrassing moment during the night, and then when you're hungover. I get that quite a bit. So, not only am I hungover from too much alcohol, I have a comedown, and I can't look in the mirror cause I did some really dumb shit I'm ashamed off. I HATE those Sundays.