Paul Dano had sleepless nights filming 'The Batman'

Paul Dano suffered sleepless nights while filming 'The Batman'.

The 37-year-old actor portrays the Riddler in the upcoming film and he admitted he found it "a little hard" to step away from the menacing character at the end of a day's filming because he needed to sustain a high level of energy.

He told Entertainment Weekly magazine: “There were some nights around that I probably didn’t sleep as well as I would’ve wanted to just because it was a little hard to come down from this character.

“It takes a lot of energy to get there. And so you almost have to sustain it once you’re there because going up and down is kind of hard.

“What I felt was the opportunity that [director] Matt [Reeves] was giving with a villain in this film was more real, potentially more terrifying.”

When in character, Paul wrapped himself in plastic wrap because the Riddler didn't want to leave his DNA behind at crime scenes and he admitted he was "scared" of how his body felt afterwards.

He recalled: “My head was just throbbing with heat.

“I went home that night, after the first full day in that, and I almost couldn’t sleep because I was scared of what was happening to my head. It was like compressed from the sweat and the heat and the lack of oxygen. It was a crazy feeling.”

Paul had always wanted to make a superhero movie but nothing had caught his eye until director Matt Reeves got in touch about 'The Batman'.

He said: "[I was] waiting for the right one or ones, where you're in collaboration with people and material that excites you. And this was definitely that.

"I was totally surprised, frankly, that [the script] was so good. I felt immediately [on] page one, page two, you could tell that the director was seeing the film that they wrote.

"You could feel, even in the action scenes, the type of energy behind the fighting or the violence, it was just very fully conceived."