The 18-year-old singer-and-actress - who announced she was quitting her Disney show `Sonny with a Chance` on 19.04.11 - underwent three months of treatment for an eating disorder until January, and while in the residential clinic she discovered she was bipolar.
She told People magazine: "I never found out until I went into treatment that I was bipolar. Looking back it makes sense. There were times when I was so manic, I was writing seven songs in one night and I`d be up until 05.30 in the morning. I feel like I am in control now where my whole life wasn`t in control."
The teen star is now dedicated to helping other people as a result of her time in a clinic.
She said: "What`s important to me now is to help others."
Demi recently revealed she felt "proud" of Welsh actress Catherine Zeta-Jones, who recently underwent treatment for Bipolar II disorder.
She wrote on twitter: "I don`t know Catherine Zeta-Jones personally but what she has decided to do it SO brave.. And SO difficult but worth it... I`m proud of her (sic)"