From NY Times article, November 4, 2007:
It all tied him in knots. “I stressed out a little too much,” Mr. Ledger said.
He tends to do that. He is here in London filming the latest episode of the “Batman” franchise, “The Dark Knight.” (Mr. Bale, as it happens, plays Batman; Mr. Ledger plays the Joker.) It is a physically and mentally draining role — his Joker is a “psychopathic, mass-murdering, schizophrenic clown with zero empathy” he said cheerfully — and, as often happens when he throws himself into a part, he is not sleeping much.
“Last week I probably slept an average of two hours a night,” he said. “I couldn’t stop thinking. My body was exhausted, and my mind was still going.” One night he took an Ambien, which failed to work. He took a second one and fell into a stupor, only to wake up an hour later, his mind still racing.
Even as he spoke, Mr. Ledger was hard-pressed to keep still. He got up and poured more coffee. He stepped outside into the courtyard and smoked a cigarette. He shook his hair out from under its hood, put a rubber band around it, took out the rubber band, put on a hat, took off the hat, put the hood back up. He went outside and had another cigarette. Polite and charming, he nonetheless gave off the sense that the last thing he wanted to do was delve deep into himself for public consumption. “It can be a little distressing to have to overintellectualize yourself,” is how he put it, a little apologetically. [NY Times–Sign in required]