The Little Mix star says she attempted suicide after online abuse left her unable to "tolerate the pain anymore".
Nelson, 28, became famous after auditioning for The X Factor as a solo act and instead being matched with Leigh-Anne Pinnock, Perrie Edwards and Jade Thirlwall to form a group.
Soon afterwards, she became "obsessed" with reading negative comments about herself online.
She told The Guardian: "It only got worse when I got Twitter. And that led to the Daily Mail, and reading the [below the line] comments - the worst you can read about yourself.
"It was like I purposely wanted to hurt myself."
"I had a routine of waking up, going on Twitter, searching for the worst things I could about myself," she added.
"I'd type in the search bar, 'Jesy fat', or 'Jesy ugly', and see what would come up. Sometimes I didn't even need to do that, I'd just write 'Jesy' and then I'd see all the horrible things.
"Everyone told me to ignore it - but it was like an addiction."
She said she would try to starve herself before performances and then binge on food later.
In 2013, she hit her lowest point and tried to end her life.
"I felt that I physically couldn't tolerate the pain any more," she said.
It was only after Little Mix toured with US star Demi Lovato that things started to change for Nelson.
Some of Lovato's dancers encouraged her to quit Twitter.
She said: "It was a long, hard process, because I didn't want to help myself.
"But it wasn't until I deleted Twitter that everything changed for me and I slowly started to feel normal again."
Nelson said she still has bad days but "instead of beating myself up about it and being miserable, I think, 'OK, I'm going to have my moment of being sad, and I'll be over it".
"Before, I didn't let myself be sad," she added.
She is also planning a documentary exploring body image and mental health in the hope of making "a change and a difference to other people's lives".