Friend hangover: feelings of sadness and depression after being separated from your best friends. Occurs mostly after having spent multiple fun-filled days together and then being forced to go back to your everyday lives. Friend hangovers occur most commonly with friends who live in different places and are thus separated often.
I'm suffering from a friend hangover today after an amazing weekend with some of my best girlfriends. Cheers to seeing each other again (& more sleepovers) in three and a half weeks!