Aneurin Barnard has revealed that he stepped into an agoraphobic's shoes for the whole time he was shooting Citadel.
The Welsh star - who currently appears in Elfie Hopkins alongside Jaime Winstone - plays an agoraphobic father in Ciaran Foy's thriller.
"It is a film which I literally poured my heart and soul into, because I had to live it for over two months. It's very difficult to play an agoraphobic, especially with a baby, and the film goes into different worlds, which makes you hyperventilate constantly," he said.
Citadel, which the actor describes as "an under-the-skin thriller", had its world premiere at Texas festival SXSW, where it won the Midnighters Audience Award.
Aneurin told how he took the time to prepare for the role.
He said: "I spent time with some agoraphobics and I went to see therapists, who work with people suffering from it. I had to do my research - I read about it, found out the physical side of it, how it happened and what happens in their bodies. It's very interesting.
"There are many different forms of agoraphobia, but we went for the most extreme version."
Aneurin, who would like to work with Dame Judi Dench and Sir Anthony Hopkins, may have made his name in musical Spring Awakening and BBC Four film We'll Take Manhattan, where he played photographer David Bailey, but said he'd love to indulge his action side.
"I love doing my own stunts. I'd love to do a full-on period sword-fighting piece where I get to show off with fighting and horses - I'm up for it," he said.