It's... something that just happens. Sort of a combination between realizing people have been laughing at rather than with you and some other stuff, IIRC.
It does always make me feel physically and mentally drained in addition to usually being emotionally drained because I go from being a bombastic, large ham ass to being THE bombastic, largest ham butt of doom when I've been inebriated. So I imagine others must experience something of that draining which would contribute to such blahness.
Plenty of water for you, young man.