"Paris has been very, very depressed for a while. She's been throwing fits and tantrums, kicking and screaming and cutting herself," says the source.
PEOPLE has confirmed that Jackson, 15, cut her wrists with a kitchen knife and took as many as 20 ibuprofen tablets, and is now stabilized at a Southern California hospital.
"She misses her father greatly," the source adds. (June 25 marks the fourth anniversary of Michael Jackson's death.) "She was the center of Michael's world and it's all different now. She says that she is lonely and that she doesn't feel loved."
Katherine Jackson's attorney Sandra Ribera, who confirms that Paris is now "physically fine" and getting medical attention, adds, "Being a sensitive 15-year-old is difficult no matter who you are. It is especially difficult when you lose the person closest to you."
Paris, who's recently been connecting with her mother, Debbie Rowe, may initially have appeared to be acting out – the tipping point, says the family source, may have been when Paris wasn't allowed to go to a Marilyn Manson concert (he's performing in her area Thursday).
Mark J. Terrill / AP
A second source familiar with the situation echoed the cry for help sentiment and says, "Paris is very unhappy and alone. She's living in this place and there's security and uncles and all these hangers-on. And she's alone. That's one of the reasons she reached out to Debbie Rowe – she wants a family, she's missed her dad."
And while her grandmother (and legal co-guardian) Katherine has been very supportive of Paris's ongoing relationship with Rowe, recently Paris has felt pressures outside the family. She signed with a manager and has been flooded with offers to work but hasn't wanted to commit, says the first family source.
Some recent Tweets from the teenager might also provide insight to her state of mind. "The day is halfway over I need to get out of bed ugh," she wrote on June 2, along with: "every time i try to distract myself it never works and I end up making the same mistake i make every single night …"
And most recently, she Tweeted a line from The Beatles' "Yesterday" early Wednesday morning.
"Yesterday, all my troubles seemed so far away now it looks as though they're here to stay."
Additional reporting by JD HEYMAN