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.