Chyler Leigh has faced a "very, very difficult journey" with bipolar disorder.
The 'Supergirl' actress was diagnosed with the mental health condition 10 years ago and had seen firsthand how "extreme" symptoms can get without taking care of herself because her mother was also a sufferer.
She said: "My mother was diagnosed with -- at the time they were calling it manic depression -- and I saw such an extreme version.
"Because I saw what happens when you aren't advocating for yourself or taking care of yourself, when I first got the bipolar diagnosis it was sort of like, 'Oh my gosh, if that was me, how on Earth am I going to deal with this?' Am I in the same place? Am I equipped? Do I have what it takes to actually really genuinely take care of myself?' "
The 37-year-old star - who has three children with husband Nathan West - admitted she felt like she was "drowning" before she received her diagnosis after hitting "breaking point" with her career and family.
She told People magazine: "We have three kids that are also living with either a mental health condition -- we have ADHD, we have Asperger's, high-functioning autism -- that's all of my three kids.
"So that, [and my] career, trying to make [our] marriage work, dealing with all these symptoms and not knowing what to do with it, that's where I kinda hit my breaking point and I shut down completely.
"During that point, right before I was diagnosed, I was like, 'I'm drowning, I'm drowning.'"
Chyler is usually "very private" because she doesn't want to be judged but has decided to speak out now as part of the Be Vocal: Speak Up for Mental Health campaign.
She said: "I've always been a very kind of private person. I think mostly because of being afraid of having my story out there and being labelled as anything because there is very often such a negative stigma about it.
"That fear of judgment and 'Oh, if people see me this way, that means that I'm not good enough or I'm not well enough to be able to take care of myself' or whatever it might be.
"But, being able to have a fantastic platform to be able to speak my story and know that it's going to reach a tremendous amount of people, that was major motivation for me [to speak out]."