The singer delves into her struggles both personally and professionally in her new book, "Finding Your Harmony: Dream Big, Have Faith, and Achieve More Than You Can Imagine", and reveals she fell into a "dark place" after she was repeatedly sidelined for solo verses on a number of the girl group's singles.
Discussing how she "wasn't allowed to use my voice figuratively and literally," she explained to People.com, "I didn't feel like I was allowed to be myself, I wasn't allowed to speak my mind. I felt alone."
Ally tried to hide her unhappiness to live up to fans' perception of her role as the happy, big sister of the band.
"The fans would call me their sunshine and I felt it was my duty and my responsibility - no matter what happened - to go out and smile," the 27-year-old shared. "I tried to be that for a very long time but it took a toll behind the scenes when the lights would go off."
Ally found herself stuck in the "unfair" situation, and resorted to booze: "My whole world just came crashing down," she recalled of the tough time, without sharing specifics. "The pressure to be perfect, the pressure to pretend that things were okay when they weren't, it got to me."
"I felt like I couldn't talk to anybody. And when you mix all of that, it's the perfect concoction for disaster and for self-destruction."
And one alcohol-fuelled night almost ended in her hospitalisation: "I think if I had one more drink I would have definitely ended up in the hospital," she said, admitting Fifth Harmony's tour manager, Will Bracey, came to her rescue after forcing his way into her hotel room, where he found her in a complete mess as she asked, "Why is this happening to me?".
"He reminded me that God is greater than all of my problems," she continued. "And even though my problems were very real, that God was going to create a way back to the light. And God did do that."
Fifth Harmony went on hiatus in 2018, and Brooke is now building up her own solo career, as both a singer and an actress.
She is currently on location in Atlanta, Georgia, filming her first movie, "High Expectations", while her new single, "What Are We Waiting For?", drops on Friday, October 16.
"I'm so happy that now I can feel free to be who I want to be," she gushed. "I'm the happiest I've ever been."