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By now, sadly, it is a familiar sight: Britney Spears, driving around L.A. in the pitch dark with her lights off, engulfed by a meteor shower of paparazzi flashbulbs. On Jan. 7, hobbled by a flat tire and wreaking mayhem on L.A. traffic, a smiling Spears—in a slinky silk top and red boots—and her assistant Karla finally ditched their Mercedes on the street (police later impounded it) and hitched a ride home in a lensman's car. After listening to Timbaland's Shock Value on the drive back, "when we got back to her house, she took her sunglasses off, and she just seemed normal," says Fabricio Mariotto, a photographer for X 17 agency. "She has pictures of her and the kids in the living room. She handed me her keys and asked me to please take care of her car. She was very nice."

So went another round in the unsettling life of Britney Spears, wherein paparazzi serve as both cavalry and companions, the road is often dark and the shockingly unexpected lurks at every turn. Just four nights earlier, amid another lightning storm of flashbulbs, a far more dire scenario had played out before the world: a wild-eyed Spears, 26, being carried out of her Studio City home on a gurney, her bare feet strapped down. In those raw moments, Spears—a mother, a daughter and a once-blazing pop star who has sold more than 70 million albums—appeared, above all else, to be a woman in crisis. "The images of her from the ambulance startled everyone who knows her," says a source. "She looked manic." Her family "is terrified," says a Spears family friend. With the singer continuing to shun longtime friends and relatives, "everyone has been worried for some time," says the source. "Her world has been crumbling around her."

As the unfolding drama rapidly made the rounds everywhere from blogs to beauty shops, the questions seemed to be: How did the once-sparkling singer with the homespun charm and earnest enthusiasm fall so far, and so hard—and what can be done to help her? Several sources tell PEOPLE that the ordeal and its dramatic aftermath—Spears has been stripped of all visitation rights to her children until at least Jan. 14—are the results of a long-gestating mental illness. "She's suffered from a psychological disease for years," says a source close to the singer. Two separate sources close to Spears believe she has been diagnosed as bipolar, while additional sources confirm she has been prescribed at least one antidepressant/antianxiety drug. Dr. Mark Goulston, a Santa Monica-based psychiatrist who has not treated Spears, says her erratic actions both in the past week and in recent years (see timeline) suggest "classic bipolar behavior, including hypersexuality, poor judgment and impulsivity." Minor behaviors that once seemed merely quirky—the hot-pink wigs, occasional British accent, barefoot bathroom pit stops, as well as major incidents such as shaving her head in early 2007—take on new context when viewed through a prism of possible mental illness. Yet "she does not think she has a problem," says a source close to Spears. Dr. Goulston points out that "manic behavior is when you don't have any sense of rules. There's a grandiosity: 'I play by my own rules.'"

By all accounts the circumstances of that now-infamous Jan. 3 night are harrowing: After a scheduled visitation with sons Preston, 2, and Jayden, 16 months, was up—as usual, ex-husband Kevin Federline's bodyguard had come to retrieve the children—Spears locked herself in a bathroom with Jayden, where she was "screaming out the window while Jayden cried," says a source. (Preston had already been strapped into the car when the ordeal began and "wasn't really aware of anything that was going on, thank goodness," says a source.) Federline's attorney Mark Vincent Kaplan was summoned to provide police with the court's visitation order. The scene at the house "was intense—no doubt about that," says Kaplan.

The four-hour standoff finally ended with police breaking down the door. Paramedics then restrained Spears and delivered her to Cedars-Sinai Medical Center, where she was forcibly committed for evaluation under California's 5150 Hold, in which a medical professional deemed Spears a danger to herself or others. (Per protocol Jayden also was taken to the hospital but was not injured.) Once there Spears was "causing a ruckus ... like a caged prisoner," says a source familiar with the situation. Then, in perhaps the saga's most shocking turn of events, Spears—who had been expected to remain hospitalized for a standard 72 hours—was released after just one day, much to the dismay of horrified friends and family. Dad Jamie Spears, 55, "was in tears," says a source. (Dr. Phil, who has been in contact with the Spears clan, later cancelled a planned episode on Spears "out of consideration for the family.")

Meanwhile, Spears' mom, Lynne, 52, and pregnant sister Jamie Lynn, 16, anxiously watched the situation unravel from the family's home base in Kentwood, La. Says Britney's aunt Linda Ann Brandon-Kjos: "It was very upsetting. We are just praying for her." Adds Britney's former assistant Felicia Culotta: "My heart and prayers are with her and her family."

Also blindsided: Federline, 29, who just hours before his ex-wife's implosion was relaxed and optimistic about the new year during an interview and photo shoot with PEOPLE. Still, speaking about his upcoming stint on the CW's One Tree Hill, he noted of his character's fate on the show, "it's not death. What would that do to the kids if they saw Daddy die? It's not happening."

Following the events of Jan. 3, Federline "is sad; he's upset," says a source close to him. "His tight circle is even tighter." The police, in fact, placed a five-day restraining order against Spears, and Federline bulked up security at his Tarzana home, where he spent much of the weekend watching football, and a longtime nanny helped care for the boys.

Meanwhile, the Spears-Federline custody battle is even more snarled than ever: Already complicated by Spears' continued failure to comply with court orders—the morning of Jan. 3 she had shown up more than an hour and a half late to a deposition with Kaplan (see box)—the case remains a complex one: "There are a lot of balls in the air right now," says Kaplan.

Also at issue is the question of what role, if any, drugs and alcohol are playing in Spears' troubles. According to Dr. Diana Kirschner, who has not treated Spears, "people who show patterns of behavior like Britney are suffering from a dual diagnosis. They have both a substance abuse problem and a bipolar disorder or manic disorder." (In September Spears was characterized by the court in her custody case to be a "habitual, frequent, and continuous" user of drugs.) L.A. police said Spears appeared to be under the influence of "an unknown substance" during the ordeal, and she was drug tested when she was admitted to Cedars-Sinai. A reliable source says, "When you take prescription meds, that will show up in a test. But what we're talking about here is illegal drugs and alcohol, and for that she has tested clean." As for reports that she was suicidal, "this is really a matter of her being unstable, not suicidal," says another source. "She's not balanced."

It's hardly the way folks back in Kentwood, La., remember the bubbly young Spears. Growing up, "she was the sweetest, most mannerly little girl in the world," says a family friend. But her home life wasn't always stable: After her parents divorced in 2002, she called it "the best thing that's ever happened to my family." Troubles have plagued the paternal side of her family tree as well: Her grandmother Emma Spears shot herself to death at 31; Jamie has battled alcohol problems. Still, says Britney's former dance teacher and family friend Renee Donewar, "I've never heard anyone talk about there being a history of mental illness in her family or making a big deal about it at all."

Of course, from her pig-tailed beginnings as a tween idol to her evolution as a sexy superstar and then newlywed and new mom, Spears has weathered nearly every triumph—and misstep—in the public eye. But this latest, gravest saga may have its roots in the postpartum depression Spears suffered after the births of her two boys, say several sources. "She would be sweet and happy sometimes, and the next minute she would explode and demand her way and then be depressed," says a source who was close to the family during her marriage. "She wasn't manic while I was there, but she was depressed a lot," says a former nanny. "She would say, 'The only time I feel relaxed is when I've had a drink.' She started reading Brooke Shields' book [on postpartum depression]." Adds another source: "When [she and Kevin] announced they were pregnant, I was worried. She was a genuinely sweet person, but she related to her [then] 13-year-old sister the most. She still seemed like a little girl." The '06 breakup of her marriage only worsened things, adds this source: "Once they started having problems, the mania started showing. As soon as the one close relationship in her life started to deteriorate, she started to deteriorate."

Things had gotten so bad early last year that her family even staged an intervention, planned by her then-manager Larry Rudolph. "Her mom, brother [Bryan, 30], dad, sister were all there," says a source. "[The intervention] was about everything: her work, her partying, just her choices in general." But if anything, the attempt merely created further distance between Spears and her family—not unusual among those with mental illness such as bipolar disorder, says Dr. Goulston. "As soon as people like this feel like you're trying to control them, you can't help them," he says. (Other Spears companions, including Sam Lutfi and Alli Sims, seem to be in her life more sporadically of late, and her recent relationship with photographer Adnan Ghalib, 35, "is her rebellious thing," says a source. "She lets him in because she thinks it pisses people off.")

And so, the young mother who, when asked by PEOPLE in '06 what kept her grounded, replied, "family, family, family," is now cut off from nearly everyone whom she once held close—including, most devastatingly, her own children. They're too young to understand what is going on, but old enough to long for their mother. "It is very, very sad," says a family friend. "If she doesn't get help," adds Doreen Seal, the mother of Jason Alexander, the childhood pal briefly married to Britney in '04, "I don't think anybody wants to see the way this will end."

  • Contributors:
  • Reported by Bryan Alexander,
  • Pernilla Cedenheim,
  • Alicia Dennis,
  • Jennifer Garcia,
  • Steve Helling,
  • Ruth Laney,
  • Marisa Laudadio,
  • Ken Lee,
  • Mary Margaret,
  • Ryan Pienciak.