The 22-year-old star said she struggled with anxiety and depression in her childhood, which led her to self-harm, reported Vogue.
"This is something I haven't been open about, but it's a huge part of who I am. All of a sudden I was hit with a massive wave of depression and anxiety and self-hatred, where the feelings were so painful that I would slam my head against a tree to try to knock myself out," the "Paper Towns" actress said.
"I never cut, but I'd scratch myself to the point of bleeding. I just wanted to dematerialise and have someone sweep me away."
"The worst thing was that I knew I was a lucky girl, and the fact that you would rather be dead... You just feel so guilty for those feelings, and it's this vicious circle. Like, how dare I feel that way? So you just attack yourself some more," she added.