When a person has spent so long on facebook they can't take it anymore.
"Dude how long have you been on facebook?"
"I dunno but I am faced-out"
(fAst'-owt) v. to be passed out or otherwise non-coherent or unconscious due to the over consumption of alcohol or illicit substances and/or from having been awake for so long from taking illicit substances that your body can no longer function awake.
See also, cracked out.
Dude, Mo drank three Tokyo Teas and no one knew she was drunk until on the way home she started barfing out the car window! When she got home she ended up faced-out on the bathroom floor.