Co-host Myleene Klass rushed to her aid, and put the 27-year-old into the recovery position until a medical professional arrived.
The singer grasped the microphone stand as she fell to the floor
Rebecca has since reassured her worried fans, tweeting, "I am feeling much better, will rest today so sorry to worry everybody I fought through that song but at the end had nothing left. Love yas xxx."
A spokesperson for Loose Women confirmed, "Rebecca became unwell during her performance on the show today. She was seen by a nurse at the studios and is fine now."
Liverpool-born Rebecca had revealed she was feeling unwell the day before her appearance. "Still laid up in bed, dunno what this bug is but it's getting shaken off big tomorrow xxx," she wrote on Twitter.
The singer complained about feeling dizzy previous to the performance
Her collapse comes shortly after the singer revealed to the Metro that she had had a tumultuous 18 months.
"I had stalkers, court cases, every crazy person you could think of was on my case," said the mum-of-two, who finished second to Matt Cardle in the 2010 series of The X Factor.
"I was going through the mill and finally got to the end and thought, 'Life is too short to stress and worry and be anxious.' You have to be thankful for the blessings you have."