Lindsay Lohan spent her first night in rehab doing something completely normal -- and completely out of character. The proactive decision-making perpetual party girl camped out Wednesday night in the reassuring glow of the boob tube and watched tone-deaf schmos embarrass themselves in front of millions.

Video: Lohan checks into rehab

"I'm doing so great, thanks," Lindsay informed the concerned OK! magazine reporter who rang her suite at the Wonderland Center in Los Angeles. "I'm fine. Nothing to worry about. Thank you so much for checking in, I do appreciate it. I'm actually watching 'American Idol' at the moment and laughing so hard!"

So just what prompted the AA-attending actress, 20, to take a major step in the often bumpy road to recovery?

According to the New York Post, she checked into the facility after pulling a post-Golden Globes all-nighter. Spies tell the paper she soaked up the scene at Prince's shindig at the Beverly Wilshire until 6 a.m., and was eventually "found passed out in a hotel hallway."

Adds an eyewitness to Us Weekly of her demeanor at the party, "She was totally out of it."

Star, meanwhile, says LiLo's trip to the $1,750-a-day rehab center came on the heels of an intervention by her family and worried execs from her in-production drama, "I Know Who Killed Me," in which she plays a pole-dancing stripper.

"The movie executives said they had a major issue with getting her insured for the film and threatened to sue her for between $3 million and $5 million for the delays her constant absences were causing on the set," a well-informed mole tattles to the tab. "Lindsay's family and other people she works with sat down ... and convinced her she had to go into rehab to save herself professionally and personally. She couldn't afford to have another letter come out about how she was being unprofessional and missing work on the set."

You'll recall that last July, Morgan Creek bigwig James Robinson publicly called out Lohan as "discourteous, irresponsible and unprofessional" for her repeated tardiness and no-shows on the set of "Georgia Rule," which he blamed on her "all-night heavy partying."

But just as she did back then, Lohan's mom-manager Dina is quick to defend the behavior of her seemingly spiraling offspring.

"I'm so proud of her," gushes Dina of her daughter's rehab check-in. "She's really in a good place right now, spiritually and mentally. She's in an amazing, phenomenal place. She's 20 and she's solid, and she's doing what she needs to do. I don't know that many people who are that secure. It's all about her, and getting back on track. She's fine -- she's amazingly fine."

But Star says Lindsay hasn't been all that "amazingly fine" since her quick trip to the hospital on Jan. 5 for a purported appendectomy, alleging she's been in "rapid decline, health-wise."

"She left the hospital with several painkillers on her; that was her downfall," a source claims to the mag. "She was using the painkillers and continuing to go out and drink. She woke up each morning exhausted and feeling sicker than ever."

Lindsay is expected to remain in rehab for at least 30 days, with the first week devoted to "detoxification," an insider tells TMZ.com.

As for the state of "I Know Who Killed Me," People reports production has been stalled since her surgery, although Star says Lohan will be permitted to leave Wonderland during the day to continue work on the flick.

And because no LiLo story would be complete without some discussion about her ensemble, Us helpfully reveals she donned black tights, a green flannel shirt, leather jacket, baseball cap and Balenciaga bag for her trip to rehab.

No word on what she had on underneath, although gossip maven Liz Smith strangely reveals how disappointed she is that the starlet's recent purchase of red undies reading "Clean" on one side and "Sober" on the other didn't make a lasting impression.