The mental state
you exist in the day after a serious drinking session
when you wake up with no recollection of anything that happened.
As the day wears on, usually starting with getting out of bed to put on the coffee you get hit with a series of emotional DOH!s as pieces of last night float back into your mind and you begin to recall some of the things you said and some of the people you said them to
Serious emotional hangovers occur mostly in relation to works nights out when you recall telling one of the VP's exactly what your opinions are of the drivel that is the company's mission statement. They also occur following nights out where your ex was in the same bar, the one you've been trying to convince yourself you were over but last night begged on bended knee to get back together with. Only to be pointed in the direction of their new love, who disturbingly is not the same sex as you.
Outside of socialising emotional hangovers also include recalling the voice mail you left your ex when you got back home, detailing all their faults the first five minutes and promising unrequieted love if they return to you for the last five, finishing with a slow sobbing down the phone and a threat of suicide.
Emotional hangovers can, as you get older, include various actions that you took. Normally for younger people these are fairly acceptable and not something to be embarassed about, but for those who are meant to be more mature it is never easy when you get a flashback of you standing on top of the bar lighting your farts in front of everyone.