Demi Lovato revealed that she had bipolar disorder diagnosed last year when she entered rehab, as Jen noted in the morning mix. “I was actually manic a lot of the times that I would take on workloads,” the young starlet told “Good Morning America” in an interview that was filmed a few weeks ago. “I was conquering the world, but then I would come crashing down. And I’d be more depressed than ever.”

The 18-year-old Disney star entered rehab in the fall for treatment of an eating disorder, which she told “GMA” was caused by bullying. Lovato, who will not return to her Disney Show, “Sonny With a Chance,” said she would cut herself when she was depressed.

Lovato, who filmed a PSA with Seventeen Magazine and the Jed Foundation urging young girls to seek help for depression, said she thought of her younger sister, Madison, to help her through treatment.

The full interview will air on “20/20” Friday: