Demi Lovato feared she had overdosed on drugs when she relapsed during her stint in rehab.

The 25-year-old singer has admitted when she checked into a rehabilitation centre in 2010 to help her overcome her battle with substance abuse she was not ''ready to get sober'', which saw her smuggle drugs around with her.

Speaking openly about her struggle on her new documentary titled 'Simply Complicated', the 'Heart Attack' artist said: ''I wasn't working my program, I wasn't ready to get sober. I was sneaking [cocaine] on planes, I was sneaking it in bathrooms, sneaking it throughout the night ... I went on a bender of like, two months where I was using daily.''

And the star has revealed there even came a point where she feared for her life after she took a ''bunch'' of cocaine.

She explained: ''There was one night when I used a bunch of coke and I popped a few Xanax bars, and I began to choke a little bit. My heart started racing, and I thought to myself, 'Oh my God, I might be overdosing right now'.''

The 'Sorry Not Sorry' hitmaker has admitted she was still taking drugs when she had a ''sober companion'' and would ''fake'' her tests.

She continued: ''I was using while I had a sober companion. And I went through about 20 different sober companions.

''I would sneak out and get drugs, I would fake my drug tests with other people's pee.''

But it was the fear of losing her loved ones that encouraged the 'Camp Rock' actress to try harder to be sober.

Demi's sober coach Mike Bayer explained: ''The most important thing to Demi is losing people, losing people that she cares about and that love her.''

The brunette beauty has admitted she is embarrassed when she reflects on her former self.

She said: ''It's embarrassing to look back on the person that I was. I think that approach worked for me because ... it was the beginning of the process of surrendering.''