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."