Hannah Waddingham battled a difficult acting experience. 

The Game of Thrones actress—who appeared as Septa Unella on seasons five and six of the hit HBO series—shared that she experienced trauma from filming a scene in which her character is tortured by Gregor "The Mountain" Clegane, played by Hafþór Júlíus Björnsson. 

"Thrones gave me something I wasn't expecting from it," Hannah explained during an April 2 appearance on The Late Show with Stephen Colbert, "and that is chronic claustrophobia."

The Ted Lasso star went on to describe the specific season six moment that spurred on her fear, explaining that it was "10 hours" of her "being actually waterboarded."

"I'm strapped to a table with leather straps," she detailed, adding that the bands were so that she couldn't lift up her head—because she thought it wuld be "too obvious" to viewers if the straps were loose. 

When the scene finally wrapped, Hannah recalled being physically and emotionally drained. 

"I had grape juice all in my hair, so it went purple," she remembered. "I couldn't speak because the Mountain had his hand over my mouth because I was screaming, and I had strap marks everywhere like I'd been attacked."

And while the experience has had a lasting impact on Hannah, the 49-year-old said she's since told Game of Thrones co-creators David Benioff and Dan Weiss that the caliber of the show made it worth it. 

"I was like, ‘Good job it's for them because it was horrific,'" Hannah explained. "The reason why I don't believe it's touched yet, in terms of the cinematography for a series, is it's just a different level."

She added, "It kind of doesn't matter when you're in Thrones, because you just want to give the best."

And considering the challenges of filming the show, Game of Thrones director of photographer Robert McLachlan previously shared some of the safety precautions they took to protect actors, including using safety cables for stunts and having a health and safety officer from HBO advise them on set.

"If anything, while the show has gotten bigger, in a lot of ways the running of it just gets smoother and smoother because everybody is so familiar with it," Robert told Business Insider in an interview published in 2017. "Along with the amazing, collaborative, creative culture of excellence that's fostered, it starts right at the top and it goes all the way down. It's one of the most committed and professional and dedicated crews I've worked with."