The direct translation from the Norwegian word fylleangst. It is the horrible mix of feelings you get after a really drunk (typical Norwegian) night out and you might or might not remember what you have done. If you remember, the feelings are there because you were so stupid. And if you don't remember it is usually even worse because you have no idea of what has been done or said and the only clues you have are for example pictures found on your (or others') cameras/phones or items found in jacket/purse/on the floor. Or in your bed. The feelings may vary between extreme embarrasment, regret and pure anxiety (especially if the memory is blank). Doubts about whether friendships are still friendships may also arise - and also doubts regarding your own dignity and selfworth.
Waking up after a really wet night, realizing that you are wearing someone elses underwear and you cannot find yours neither remember how you got that pair on. The first feeling apart from the nausea from the hangover is the wasted-anxiety that makes you want to just stay in bed for a week. Apart from the fact that it's not your bed and you just want to get the hell out of there, which increases the wasted-anxiety to maximum level.