Mariah Carey revealed her struggles with bipolar disorder in a new People cover story, telling the magazine she “didn’t want to believe it” after being hospitalized and diagnosed in 2001 following a mental and physical breakdown. The singer noted that she recently received treatment after enduring “the hardest couple of years [she’d] been through,” which included professional woes, the cancellation of her E! reality show, Mariah’s World, and separating from her fiancé.

The platinum-selling pop star told People that, until recently, she “lived in denial and isolation and in constant fear that someone would expose” her illness. “It was too heavy a burden to carry, and I simply couldn’t do that anymore,” she said. “I sought and received treatment; I put positive people around me, and I got back to doing what I love – writing songs and making music.”

Carey was diagnosed with bipolar II disorder, characterized by depression and hypomania. The vocalist is attending therapy and taking a medication she claims has been helping without significant side effects.

The singer – who has landed 18 Number One singles on the Billboard Hot 100, the highest amount for any solo artist – told People that she first pegged her illness as a “severe sleep disorder,” but she realized her issues ran deeper than insomnia. “I was irritable and in constant fear of letting people down,” she said. “It turns out that I was experiencing a form of mania. Eventually I would just hit a wall. I guess my depressive episodes were characterized by having very low energy. I would feel so lonely and sad — even guilty that I wasn’t doing what I needed to be doing for my career.”

Carey, who is reportedly working on a new solo LP expected later this year, opened up last year about battling deep self-esteem issues since childhood. “Growing up different, being biracial, having the whole thing where I did not know if I fit in,” she told New York Post‘s Page Six before a concert at Madison Square Garden. “That is why music became such a big part of my life, because it helped me overcome those issues,” she said. “Sometimes it is hard to let your guard down.”

Last July, the Starz network announced plans to create a fictional drama series based on Carey’s life. Brett Ratner, best known for directing the Rush Hour film franchise, is set to executive produce alongside the singer.