The Undoing took both a physical and mental toll on Nicole Kidman.
The 53-year-old actress portrayed therapist Grace Fraser on the 2020 whodunit drama series, whose husband Jonathan Fraser (Hugh Grant) is investigated for murder.
And Kidman has revealed she was "really sick" and struggled with a "disquietness" to her own "personality" where she couldn't tell the difference between "acting and truth" during filming.
Discussing the impact her shows, including HBO's Big Little Lies, have on her mental health, Kidman told Marc Maron's 'WTF With Marc Maron' podcast: "Even on The Undoing it kind of happened where I just like suddenly was in this place of … There was sort of a disquietness to my personality, where I was uneasy and there was duress on who I was."
She added: "I went down for a week, because your immune system it doesn't know the difference between acting and truth when you're doing them."
The Oscar-winner admitted that while other actors can make their body know the difference between acting and reality: "It doesn't really work for me."
Elsewhere, Kidman recalled another traumatic experience in her life when her Eyes Wide Shut director, Stanley Kubrick, died in 1999.
The Moulin Rouge star had received a fax from the filmmaker the night before he died asking her to give him a call, but she never got around to it.
Kidman recalled being informed of his death: "I just started screaming, I collapsed on the ground. I was that close to him.
"I have a huge fear of phone calls in the night now, because I've received a number of them with that sort of news, my father included."
The Bombshell actress' ex-husband and co-star, Tom Cruise, supported her through the trauma and she also revealed she would fly off to Sydney or Paris when she was on standby and once got caught out when Kubrick asked her to join the set in the UK.
She remembered: "Tom was like, 'Aww, we're screwed. You're going to have to call Stanley.'
"So I was like, 'Stanley, I'm sorry. I'm actually not in the house, I'm in Sydney,' and he goes, 'Unfaithful woman'."