Demi made that revelation on CBS "Sunday Morning News" while talking about her documentary film, "Dancing with the Devil" ... and she admitted, "I didn't control any of my life at that period of time. But yes, I also needed to grow up and take control."

The singer says it's really only in the last 2 years that she's changed that, and much more. Demi adds, "I'm now in control of my finances, I'm now in control of the food that I eat, how often I work out."

Demi said things got so bad with her food intake ... every time she was in a hotel room her phone was taken away from her so she wouldn't order room service.

She also opened up a little bit about her recovery, and interestingly she says she's what they call "California sober." Demi didn't dig into what that means for her -- and explained why she didn't want to say -- but that's a phrase that commonly means someone who uses a little marijuana.

As we reported ... Demi told Smith she was about 5 to 10 minutes from death after her 2018 overdose.