The 28-year-old singer was taken to hospital in Los Angeles after relapsing. She had been sober for six years.
Demi explores her battle with addiction in the YouTube documentary series Dancing With The Devil and in a new trailer shared details about her overdose.
“I had three strokes,” she said. “I had a heart attack. My doctors said that I had five to 10 more minutes.”
The US star revealed she was still living with the effects of the overdose, including brain damage and blind spots in her vision which prevent her from driving.
She said she wanted to “set the record straight” with the documentary, which features a friend telling the camera “she should be dead”.
She added: “I’ve had a lot of lives, like a cat. I’m on my ninth life.”
Sir Elton John also appears in the trailer and says: “When you’re young, and you’re famous, my God, it’s tough.”
The four-part documentary series Dancing With The Devil is directed by Michael D Ratner and promises to give fans “unprecedented access” to Demi’s recovery and career since the overdose in July 2018.
The singer, whose hits include Sorry Not Sorry and Cool For The Summer, previously described the day she almost died as her “miracle day”.
This is the third documentary featuring Demi. The 2012 film Stay Strong explored her recovery after she cancelled a tour with the Jonas Brothers to enter rehab.
In 2017’s Simply Complicated, she admitted she had been dishonest in Stay Strong and had been under the influence of cocaine during the making of the film.
Demi Lovato: Dancing With The Devil will premiere on YouTube on 23 March.
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Outside of Australia, please visit the International Association for Suicide Prevention for a database of resources.