An LAPD source tells PEOPLE: "Spears was escorted by police and is on her way to get help."
The singer, 26, was transported to UCLA for treatment and evaluation during a 72-hour emergency hold, known as a 5150.
"She went willingly. It was like something in her heart was telling her she should go. She knew something was wrong," confidant Sam Lutfi tells PEOPLE.
Police or a mental health professional can request one if a person is deemed to be a danger to herself or others. (Spears was held at Cedars-Sinai Medical Center on such an order earlier this month, following her Jan. 3 custody standoff with police.)
Spears's mother, Lynne – who's in the midst of a tense reunion with her daughter – friend Alli Sims and Lutfi were all inside the gated mansion when police and the fire department arrived.
What brought on the hospitalization? "She was driving around her neighborhood like a mad-woman," says a Spears family source. "Britney has been prescribed medication which she refuses to take. This is just another sad, sad evening."
Lutfi and Spears's father, Jamie, arrived at the hospital shortly after the singer. Her mother was later spotted leaving the Summit home with Spears's photographer beau, Adnan Ghalib, in the backseat.
Earlier in the night, Internet rumors claimed that the singer had attempted suicide, but Lutfi and Sims both denied those claims to PEOPLE.
Since the January standoff, Spears has been stripped of visitation rights for her two sons Preston, 2, and Jayden, 1. Two sources have said she suffers from a psychological disease, with one source saying, "there is no question she is bipolar... she's had manic episodes for years."
As last night's incident unfolded, a Spears source told PEOPLE simply, "Pray, please."
Reporting by JENNIFER GARCIA and MARY MARGARET
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