American actor Alex Wolff has suggested he has "some sort of PTSD" after filming the upcoming horror flick Hereditary.

Wolff plays Toni Collette's on-screen son, Peter – a character shellshocked with grief over the recent death of his maternal grandmother. At first, the film plays out like a psychological family drama. However, as with any good horror movie, things quickly start to take a sinister turn.

The film's trailer shows Wolff stumbling down a hallway while hallucinating and in another scene he is unable to stop himself from slamming his head into his school desk over and over again.

The 20-year-old is no stranger to acting, having first starred alongside his brother in the 2007 Nickelodeon comedy series The Naked Brothers Band. But it turns out nothing could have prepared him for the role of Peter Graham.

Alex Wolff at a screening of Hereditary.

Photo: AP

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Speaking to Vice, the up-and-coming Hollywood star said the film stayed with him long after the cameras stopped rolling.

"When I started talking about it, all these flashes with all this disturbing shit I went through sorta came back in a flood," he said. "I had to absorb the pain … it's hard to describe eloquently, it's just a feeling. I don't think you can go through something like this and not have some sort of PTSD afterwards.

"I spent a lot of time and phsyical preparation to keep myself in a pretty raw and volatile state while I was in the middle of filming."

Alex Wolff in a scene from the horror film.

Photo: AP

The actor admitted he'd even forgotten about some takes after shooting, possibly as a result of the focused headspace he needed to be in at the time. When it came to filming the desk-smashing scene, he volunteered for the prop to be made out of real wood – though the director quickly shut the idea down and ensured it was crafted out of rubber.

"It's weird," Wolff said. "I watched it [for] the first time and I was like, holy shit, I don't remember shooting that scene. I'm not even kidding. I was like, what the f— is going on? I don't even remember that 100 per cent. It's strange how that could all work."

Hereditary is now showing in Australian cinemas.

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