Dennis Quaid really did freak out on a movie set -- but it was the set of a "Funny or Die" video.
The site finally copped to shooting the scene with Dennis ... by posting the full video showing Dennis losing it on the director and the crew of a fictional set. But now you can see the full skit which includes some hysterical sight gags.
The video leaked earlier this week ... just showing Dennis losing his marbles. He kept tight-lipped about it when we asked him about it on Tuesday -- but his wry smile made us think something was up.
So ... not a real freak out, just real funny.