NEW YORK — Throw away your guidebook, forget making a reservation, don't pack a bag: It's best to prepare as little as possible before making the trip to Leonardo DiCaprio's "Shutter Island." The twists, turns and backflips of this Martin Scorsese-directed film — in which Leo arrives on the island to investigate a disappearance from an insane asylum — will have you questioning what is real and what is not and the nightmarish scenarios that crop up when you can no longer tell the difference between the two.

But at the film's red-carpet premiere at the Ziegfeld Theatre in New York on Wednesday, DiCaprio and his co-stars were more than happy to lend us some insight into their own deep, dark fears about the nightmares that plague them in real life.

"When I was little, I used to have a nightmare that I was abducted by aliens, after seeing 'Close Encounters of the Third Kind,' and it freaked me out," Mark Ruffalo told MTV News. "The idea that someone would come from nowhere and grab you and take you away and do anal probes and stuff on you scared the hell out of me."

As the photogs snapped like mad and the microphones of dozens of news outlets battled for the opportunity to chat with him, DiCaprio stayed cool and collected in a thin-striped suit and silvery tie. In his dream life as well, the A-lister said he exists in a state of tranquillity. "I really don't even remember my dreams," he said. "That's the weird thing about me. People talk about psychoanalysis, discovering who they are through the dream state. I have no recollection in the morning."

Sir Ben Kingsley admitted that even Oscar winners and royally honored British citizens suffer from the occasional anxiety dream. "My recurring worst nightmare, under your charming pressure, is the actor standing onstage with no clothes, no script and doesn't even know what the play is called," he said.

Co-star Emily Mortimer deals with a similar fear haunting her slumbering hours: the chance that she'll be in front of the public and seriously futz up. "I have a nightmare that I'm going to do something peculiar at an inappropriate moment," she said, "especially in high-pressure situations like on chat shows or in premieres or when I'm on the stage, I think I'm going to shout out 'F--- the Queen!' or something like that."

Not all of the "Shutter Island"-ers, though, face nightmares connected to the realistic here and now. Nellie Sciutto, a veteran of three Scorsese pics, confessed that her dreams skew more toward the very latest in pop music. "Lady Gaga music makes me a little crazy," the actress laughed. "I admire the woman, but it makes me a little nutty. I had a dream I was in sleepaway camp with Lady Gaga. That's scary to me."

Check out everything we've got on "Shutter Island."

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