The lack of joi de vivre which occurs after a particularly fun event/weekend/gathering, i.e. a hangover from fun.
BILLY: Hey Judy, why the long face?
JUDY: Well, Billy, I went to Palm Springs with my cousins last weekend and we lived it up like it was 1965. We had a four hour dinner, too many martinis to count and we danced to Sinatra tunes 'til 2am. It was great but now old man Whethers over at HQ is riding me about this marketing data and it sucks to be back at work.
BILLY: Sounds like you've got a mean funover to me.
JUDY: Yes, I do have a funover.
A play on the word "hungover."
When one comes home after doing something extremely fun, such as going on vacation or having an adventure, and is simply unable to function as a productive human being in the aftermath of such frivolousness.
Symptoms include lounging about, not getting any work done, wishing to go back to having fun, plotting to skip work/school the next day, antisocial behavior, and poor hygiene.
A funover may last between one day and a week, though residual symptoms may continue for up to months afterwards if daily stress levels are high.
Mom: Shouldn't you unpack your bags from the trip?
You: *flopped on the couch* Ugh. No. I can't do anything right now because I'm funover. When can we go back on vacation?