The actress portrays the Hollywood icon in new biopic My Week With Marilyn, and said that getting immersed in the role took its toll on her mental state.
'Sometimes you don't (switch off). Especially with Marilyn, you don't want to,' she told Elle magazine. 'In some ways I feel like she's part of me, and in some ways I feel like she's an old friend, and in some ways it feels like a crime to abandon her.
'She was someone who so needed people and was always being abandoned. I found that, playing Marilyn, I became a lot needier than I actually am as a person. I needed quite a lot from people, an embarrassing amount.'