A terrifying underwater scene in The Bourne Supremacy left actor Matt Damon literally gasping for breath in his sleep.
The movie star was reluctant to film the car crash scene in the sequel because he didn't want to spend time underwater - and he insists the panic in his eyes was for real.
The actor told Playboy magazine: "I didn't want to do that at all.
"So I wouldn't be constantly aware of how scared I am of drowning, I had to go to a pool with this great stunt guy and dive master a couple of times a week for a month or so to train me to relax underwater without an oxygen mask."
However, the lessons didn't help him sleep after he had shot the scene.
"That night I woke up probably four times gasping for breath, thinking I was drowning. It was terrible."