The Girls Aloud star checked out of rehab in November following a month of treatment, having been urged by her bandmates to seek help when they identified that she "wasn't in a good state".
"I've been told by those close to me that was when I hit my worst. I was crying hysterically," she told The Sun. "I felt ashamed, embarrassed, terrified - my emotions were all over the place. I know [my bandmates] were really worried about me."
Harding said that her alcohol dependency intensified as her relationship with the DJ broke down in September.
"I was so down but I just tried to keep busy and, to numb myself, I was drinking more. It was my way of escaping," she said.
"One minute I was deliriously happy, to the point of hysteria, and totally in denial about my problems saying, 'I'm fine, I'm fine'. The next it hit me - and when it did, it hit me hard."
Harding briefly reconciled with Crane in November before they split for good last month.
Explaining their separation, she continued: "Our lives had started to go in different directions. We'd become like passing ships. As far as our future plans were concerned, I didn't see how it would work."
> Kimberley Walsh: 'I'm proud of Sarah Harding for facing her demons'