"My life started to spin out of control in 2010 and it was a dreadful year," Vanessa told The Sun's Fabulous magazine. "I'd be out every night."
The 24-year-old singer added that her drinking habits got so bad, they began to jeopardise her career and she relied on fellow bandmate Una Foden to sing her solos for her.
"I drank vodka mainly but, to be honest, I drank anything," she said. "It massively affected the band and I felt lonely and depressed."
At the time Vanessa was single and found herself out partying while her bandmates were settled with long-term boyfriends.
Finally, as the quintet prepared for their All Fired Up tour at the end of 2011, troubled Vanessa turned to bandmate Rochelle Humes for help.
Vanessa stayed with Rochelle, who is married to former JLS singer Marvin Humes, for two weeks and abstained from drinking.
Two years on and Vanessa is happily dating stylist and darts player Gary Salter.
The Somerset-born singer also revealed that she has found a much healthier habit to keep her on track.
"I've taken up a new hobby instead, exercising," said Vanessa. "I've become obsessed with yoga and Pilates, I love it, it's so relaxing. It's so addictive."