These complications include "nausea, vomiting, and high fever," sources said.
"[We are] took it day after day," said one of the sources.
There is no information about what has led to her hospitalization.
There were reports that Lovato overdosed heroin, but a source close to the singer denied that.
Last week, a source of knowledge told CNN that Lovato plans to leave hospital after her discharge seeking treatment for substance abuse
CNN previously reported that Lovato's family and her former boyfriend, Wilmer Valderrama, had been at their side since their consignment a week ago
At the time of her obvious overdose, a representative published a statement that Lovato was "awake and with her family."
"Demi is awake and with her family, who want to thank everyone for their love, prayer and support," said Lovato's representative. "Some of the reported information is incorrect and they respectfully ask for privacy rather than speculation as their health and recovery is the most important thing right now."
Lovato was open about her struggles with dependence on cocaine and alcohol, as well as mental health issues and an eating disorder. She also sought professional help for substance abuse and entered the pulmonary clinic in 201
"You just have to take it one day at a time, some days are easier than others and some forget to drink and use, but for me I work on my physical health, which is important, but also in my mental health Health, "said Lovato, adding that she would visit her therapists twice a week. "I make sure I stay on my meds, I go to AA meetings, I do what I can physically do in the gym, I make it a priority."
In the hours following the news of her hospitalization, fans of the singer in social media tagged #HowDemiHasHelpedMe with hashtag to talk about how she and her music helped them in their own struggles.
Lovato released a single called "Sober" in June, in which she noted a relapse after six years
"I'm sorry for the fans I lost, who saw me fall again," Lovato sings the slope. "I want to be a role model, but I'm just a human I'm sorry I'm back here, I promise I'll get help."
Lovato toured and promoted her music in recent months.
She last performed on July 22 at the California Mid-State Fair in Paso Robles, California.
CNN has contacted Lovato's representative for a comment