She was brought there early Thursday morning at the request of her doctor and family, after weeks of bizarre and disturbing behavior.
It was the pop star's second such hospitalization in a month.
On The Early Show Friday, national correspondent Hattie Kauffman reported that police tried to keep Spears' Thursday trip hush-hush, but word leaked out, leading the swarm of paparazzi who followed the lengthy motorcade of police vehicles taking Spears to the hospital, and to the crush of media at the facility.
Kauffman also says tempers, including Spears', flared inside.
According to Kauffman, Spears is now classified gravely disabled, which means she's considered a danger to herself, or others, or is unable to provide for her own food, shelter, or clothing.
Her journey to the psychiatric ward began late Wednesday night.
"We first got tipped off about this at maybe 9:30, 10 o'clock, that something was wrong," X17online.com Director of Operations Bill Graham told Kauffman, "that the mother was going to be going over to the house."
"The psychiatrist said at this point, 'She's gotta go in. Call the LAPD,' " says Harvey Levin of TMZ.com.
At one in the morning Thursday, a police motorcade accompanied the ambulance taking Spears to the hospital. She had, says Kauffman, agreed to go.
"She sat on the floor," Levin says. "She told everyone to be quiet. She passed notes; she didn't want to talk."
Police tried to fool the paparazzi, by code-naming Spears "The Package" because, says Levin, "If they start saying, 'Britney Spears is on her way to the hospital' and somebody is listening to the police radio, (bam!), everything changes."
By 2:00 a.m., papparazi were all over Spears' father when he arrived at the hospital.
Within the hour, the "quiet Britney" is said to have exploded.
Levin says, "She accused her mother of sleeping with her boyfriend. I mean, she was in the middle of some kind of a pretty bad episode, screaming and swearing."
Earlier, Britney was seen buying a case of the caffeine drink Red Bull. Paparazzi say she hadn't slept since the weekend.
Says x17online's Graham, "She would make these late-night visits to all-night grocery stores and drug stores for odds and ends."
Around 4 a.m., says Kauffman, a dispute erupted between Spears' manager Sam Lutfi and her family over who was in charge of her medical care.
At 5 a.m., Spears mother left the hospital and told reporters her daughter was OK.
By 6 a.m., a judge had ordered Spears held on a 72-hour mental evaluation.
But, notes Kauffman, the drama isn't over.
"Athough she went willingly," Graham says, " ... she is not allowing any of the physicians or nurses there to administer medicine in any form to her."