‘X Factor’s’ Demi Lovato Discusses Rehab, Body Issues on ‘Katie’ (VIDEO)

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On Monday, Demi Lovato will open up to Katie Couric about the incident which sparked her family to put her into rehab.

“What happened was I made a huge mistake and I ended up hitting one of my friends who was a back-up dancer. I felt horrible, I wasn’t really in control of my emotions at the time and I was just out of control and there’s no excuse for it but it definitely showed everyone I needed to get help and I think two days later I was checking into rehab,” said the 20-year-old.

What did the singer tell Couric about her experience at the Illinois facility?

“Treatment was so difficult at first, I remember walking around saying ‘I’m in prison!’” said Lovato.

“They needed to have those strict rules in order for me to understand how sick I was,” the “Give Your Heart a Break” singer told Couric. “I also had somebody watching over me every single time I ate. And if I didn’t finish what was on my plate, and often times I would cry because I physically couldn’t stomach it and if that happened I would have to have little consequences, nothing horrible just not being able to go to the cafeteria to eat.”

Monday’s episode of Katie will also feature Lovato talking about battling both anorexia and bulimia. The pop star says her issues with her body began at an extremely young age.

“When I started having body image issues I remember being three years old in a diaper and rubbing my hand over my stomach…and I remember thinking in my head ‘I wonder if one day this will ever be flat?’” she said.

Throughout school, Lovato was often bullied about her weight to such an extent she had to leave school.

“I was bullied and they called me fat and they called me horrible things. The only way to get through it all was I left school. I called my mom crying and said ‘you have to pick me up I have to get out of here I can’t take it anymore.’”

On Thursday, Lovato visited a New York school to promote Secret deodorant’s “Mean Stinks” campaign against bullying.

Watch Lovato’s entire interview on Katie on Monday on ABC. Check your local listings for times.