The actress, a mother of three, plays a mum overwhelmed by loss after the tragic death of her young son in new movie Rabbit's Hole.
'It's the thing that I'm probably most terrified of,' Kidman said.
'So to go into that place is almost like stepping into dangerous territory. It's frightening but that's what you want to do as an actor - to tell stories and step into places that I've never been but feel are important.'
The actress also admitted that she is so in love with husband Keith Urban she cannot spend more than three days away from him.
Kidman previously said she never spent more than a week away from the country singing star.
Now she admits: 'We've get it down to three days. It keeps getting shorter and shorter. If you get married later in life there's less time so you just want to spend that time together.'