Australian actress Nicole Kidman has opened up about how the traumatic roles she has played have taken a toll on her mental health.

The latest is HBO's psychological thriller The Undoing, in which she plays the psychiatrist wife of a man accused of murder, played by British actor Hugh Grant.

Previously, the 53-year-old actress had played an abused wife in hit series Big Little Lies (2017-2019), which had similarly affected her mental state adversely.

The Oscar winner spoke candidly on the WTF With Marc Maron podcast on Tuesday (Jan 12) about how the roles seeped into her life even after she had left the set for the day.

"Even on The Undoing it kind of happened where I just was like suddenly, I was in this place, there was sort of a disquietness to my personality where I was uneasy, and there was duress on who I was," she said.

She revealed: "I actually got really sick, and I think this is a big thing that happens to actors."

"I went down for a week because your immune system doesn't know the difference between acting and truth when you're doing those," she added.

Despite her many acting awards, Kidman said: "I have not learned a technique to tell my brain and my body, 'Oh this is just acting'.

"It doesn't really work for me. I go home, and I don't sleep well and I'm not well if it's that disturbing to me."

She had spoken openly before about her struggles with not letting her intense roles and their emotions overwhelm her in her family life.

In an interview with WSJ. Magazine in March last year, she said: "Certain things penetrate psychologically in a really deep way. It does take a toll on my health and it takes a toll on my spirit."

Fortunately, her husband, singer-songwriter Keith Urban, 53, and her two young daughters are "unbelievably understanding", she said, although they don't always quite understand what's going on.

She said 12-year-old Sunday and 10-year-old Faith had asked her: "Why are you looking like that, Mummy?'"

On the flip side, her recent role in The Prom (2020), a Netflix musical comedy, gave her a lift in the spirits off the set.

"I just go, 'Great, I get to dance and I get to love everybody, and I get to go 'Come here, let me hug you, it's all gonna be all right'.''

Correction note: An earlier version of the story stated that Kidman played the role of a lawyer in The Undoing. This has been corrected.