The X Factor 2010 finalist told the Daily Star Sunday that she was forced to "toughen up a lot" over the last two years.
"I can't watch my first audition because it makes me too upset," she told the paper. "I just think it is really sad. I look at myself and don't recognise myself. I do think fame and fortune changes people."
She continued: "I have had to change because the girl in that audition wouldn't survive in the music industry. Little sweet Becki who loves everyone and who thinks the best of everyone wouldn't survive.
"I have had to toughen up a lot," she added, "so when I look at that I feel really sad."
Ferguson returns to The X Factor tonight (October 14) to perform her new single 'Backtrack'. The 26-year-old from Liverpool said that her time on the show taught her the importance of holding on to her identity.
"My advice is, if you are going to go on X Factor you have to know who you are as an artist," she explained.
"A lot of people go on, get told what to do, make a fool of themselves and then blame someone else.
"When I went on there I was asked to sing things and I used to say 'no way'," she added. "You have to know who you are as an artist. If you are not happy with the song, don't sing it. Simple as that - no-one forces you to do it."
The singer also said that she learned the hard way about the importance of a work-life balance. Earlier this year, she publicly fell out with her management company over Twitter - claiming they forced her to work to the point of collapse - and they are now suing her for breach of contract.
"I was naive in that I thought I could just sing and perform and do what I had always wanted to do all my life," she said.
"But I wasn't ready for all the added dramas that came along. There were times I fell out of love with music and thought about walking away.
"I thought I was happier when I was that girl at home in my bedroom singing into my hairbrush.
"I've had so many bad moments but the worst was when I collapsed," she continued. "Nothing is worth being ill or collapsing over.
"That's not music. Music is about making yourself happy and making other people happy."
Ferguson - who has since signed with a new management company - will release a deluxe edition of her latest album Heaven tomorrow (October 15) and plans to tour the US early next year.
"I'm just enjoying what I do again and enjoying singing again," she said.
Watch the video for Rebecca Ferguson's 'Backtrack', which is released today, below: