The Saturdays singer secretly checked into a rehab facility in 2012 after she began suffering with panic attacks and low moods and, although she kept it from her fans at the time, she has now recalled the moment she reached crisis point in her new memoir.
In the new book, 'Open: Why Asking For Help Can Save Your Life', Frankie, 31, wrote: "For as long as I can remember I had suffered from anxiety, nervousness, the big black cloud, stress, low moods, sadness.
"I lived with it in silence and tried to conquer it alone. I had trouble sleeping, lacked energy and had lost my appetite and my libido."
Frankie reached her breaking point whilst filming a music video with The Saturdays and was eventually admitted to Nightingale Hospital in London.
In the book - which is being serialised in the Daily Mail newspaper - she recalled: "As soon as I got there, doctors put me on new medication - venlafaxine, clonazepam and diphenhydramine -sleeping tablets in such high doses my first few days in hospital are a blur.
"I hadn't had a good night's rest for so long, it was a relief to silence my mind so it could just switch off. It was all I wanted, not to think, not to be inside my own brain, locked in my own painful internal battle"
Elsewhere, the 'Issues' hitmaker took the opportunity to thank her husband - then boyfriend - soccer player Wayne Bridge who admitted her into rehab.
She added: "He was my constant, the person who knew me inside out and had seen me at my worst and most vulnerable. He made me feel safe and loved. I couldn't have done it with anyone else."
Although her depression badly affected the former footballer as he dramatically lost weight due to the stress of his girlfriend's health.
Frankie continued: "Learning about my illness and realising he couldn't make me happy was a lot for him to take on. He lost a lot of weight around then and ended up the lightest he has ever been. Now we think it was due to the stress, but at the time I didn't notice how badly everything was affecting him.
"As we've spoken about my breakdown over the years since, the stress it caused him has come out in both anger and sadness."