According to TMZ, the 911 call occurred at 10:45pm, and Demi was transported by ambulances from her home after being assessed by paramedics.
Sources have told the entertainment news site that the issue is 'substance abuse,' and that Demi has been placed in a facility to "seek further professional assistance."
Demi's rep told TMZ: "Because of the stresses in her life right now, Demi has chosen to seek professional assistance to treat her exhaustion and improve her overall health. She looks forward to getting well and is grateful for the support of her family and friends."
The 49-year-old recently announced her decision to file for divorce from hubby Ashton Kutcher, after he was accused of cheating on her with 22-year-old party girl Sara Leal.
There has been growing concern over Demi's gaunt appearance for several months now.