The stars appeared together in hit Disney Channel show "Sonny With a Chance" and speaking during a virtual reunion with Thornton and fellow castmates Allisyn Ashley Arm, Doug Brochu, Sterling Knight, Audrey Whitby, Matthew Scott Montgomery, Shayne Topp, and Damien Haas, Demi reflected on her sobriety struggle since finding fame.
"When I went away to treatment for the first time, you were my biggest inspiration coming out of it because you dealt with all of those pressures of being a woman on TV," she told Tiffany. "I looked at that as, 'I wish I had that so bad.' Yes, I probably was happier in my head with whatever I looked like at the time. But I'm so much happier now with the mentality that you have."
"I look back now and I'm like, 'Man, it's a shame that we wasted any energy on what we wore on set,' " she confessed.
The "Confident" singer went on to share that, while working on the show, she "wasn't sleeping and I was so miserable and angry too because I felt like I was being overworked."
She also admitted she was a bit surprised that when she left the show, producers decided to continue without her.
"When I left, you don't expect your show to go on without you, but it did," she said. "But I couldn't have been happier for everybody... I just wasn't in a period of time when I was ready to be on camera again.
"I could not go back into that environment and there were other things that factored into it," Demi noted.
The star recently celebrated a year of sobriety following her near-fatal drug overdose in the summer of 2018, six years after previously kicking her substance abuse habit.
And Demi wonders if she would have been able to avoid the pitfalls of fame if she had chosen to step away from the spotlight after quitting "Sonny With a Chance", just like Tiffany.
"I'm realising that as I've gotten older, because when I was young, when you start off in the industry as a seven year old, eight year old, you kind of value your self-worth with your success," she explained. "I have moments all the time where I'm like, 'Do I want to continue this? Or do I want to pull a Tiffany and move to Texas, have a family and have a farm?' "