The I'm a Celebrity star believes writers destroyed her self-confidence when giving her character Rosie Webster "silly costumes".
Flanagan told the Daily Mail: "I felt people were taking the mickey out of me. I felt Rosie had become a cartoon character and I wasn't being taken seriously.
"At times, when I was asked to wear silly costumes, I felt a bit degraded and demoralised and there were times when I ran off set because I couldn't stand it anymore."
She continued: "I just wanted to be myself. I wanted to get rid of this sexy image. I felt I was being laughed at.
"I thought people at work didn't like me anymore and considered me a drama queen, a brattish diva, but I was severely depressed. I was crying my eyes out all the time.
"Eventually, someone at work pulled me aside and said, 'I really don't think you can do this anymore', because I was not well at all."
The actress pinpointed one particular moment of upset, recalling: "Once, on Corrie, I had to do this really sexy scene with loads of dialogue. I'd hardly been sleeping and couldn't concentrate so I was struggling to remember the words.
"I was wearing a bra and knickers, feeling very self-conscious, going through really bad depression. I felt knackered and just burst into tears. It was too much pressure."
Flanagan stood down from Corrie in October 2011 before her character departed Weatherfield in February 2012.