Game of Thrones was undeniably an intense show to watch.
And, apparently, to film as well. Actor Hannah Waddingham, who played Unella, a Septa of the Faith of Seven that served under the High Sparrow — we'll give you a sec to refresh your memory — recalled a certain scene she had to film that turned into "the worst day of [her] life."

In the Season 6 finale of the show, Cersei Lannister, played by Lena Headey, gets revenge on Unella for previously shaming her during the infamous walk of atonement scene.

Cersei, when she's freed, then tortures Unella by waterboarding her.
Hannah recalled getting updates about the scene as she was on her way to film, one of which being she was now required to wear a wetsuit.
"I was strapped to a wooden table with proper big straps for 10 hours. Other than childbirth, it was the worst day of my life. Lena was uncomfortable pouring liquid on my face for that long, and I was beside myself."

Hannah later told her costar Eugene Simon (Lancel Lannister) that scene was torturous to film.
"I had no voice at all to barely whisper, bruises already coming up like I'd been attacked. I was like, 'I've basically just been waterboarded for 10 hours.'"

And his response?
"Mate, I've just been crawling through shit for four days on my elbows. You haven't been in Game of Thrones unless you've been really, really battered around."
