"I didn't want to believe it," the singer-songwriter told people.com of the condition, which she was first diagnosed with in 2001.
Carey said: "Until recently I lived in denial and isolation and in constant fear someone would expose me."
"It was too heavy a burden to carry and I simply couldn't do that anymore. 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," added the Grammy winner.
One of the most successful singers of all time, Carey spent many of her years in the spotlight suffering in silence.
"I'm actually taking medication that seems to be pretty good. It's not making me feel too tired or sluggish or anything like that. Finding the proper balance is what is most important," she said.
"For a long time I thought I had a severe sleep disorder," said Carey, now back in the studio working on an album due later this year.
"But it wasn't normal insomnia and I wasn't lying awake counting sheep. I was working and working and working I was irritable and in constant fear of letting people down. It turns out that I was experiencing a form of mania.
"Eventually I would just hit a wall. I guess my depressive episodes were characterised 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," she told people.com.
Carey, who co-parents her six-year-old twin children Monroe and Moroccan with ex-husband Nick Cannon, said she decided to come forward because "I'm just in a really good place right now, where I'm comfortable discussing my struggles with bipolar II disorder".
"I'm hopeful we can get to a place where the stigma is lifted from people going through anything alone. It can be incredibly isolating. It does not have to define you and I refuse to allow it to define me or control me," she said.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)