It's reality-check time for Kristin Cavallari.

The Hills star raised eyebrows for all the wrong reasons during Super Bowl weekend in Miami: "She was wasted the entire time," a source says in the new issue of Us Weekly. "She was going around to everyone, asking them to score her some coke." (Cavallari's lawyer refutes the allegations to Us; MTV declined to comment.)

But those close to the hard-partying Cavallari, 23, say that such antics have become more and more typical. "Her issues are becoming apparent to everyone," an insider reveals. "She's getting scary-thin and not showering regularly...She's clearly unhealthy."

Her Hills friends Brody Jenner, Audrina Patridge, Lo Bosworth and Stephanie Pratt have all expressed serious concerns, but to no avail. "She doesn't think she has a problem," a source says.

And Cavallari isn't just a wild girl on her days off: the erratic, gaunt star has become chronically tardy to Hills tapings -- when she shows up at all.

In a sad twist, her struggles may even become fodder on MTV's hit show. "Her drug problem finally became an unavoidable conversation topic on film," an insider says. "If MTV uses the footage, it will be clear to everyone."

To find more about Kristin's crisis, how she's "sleeping around," her show-stopping tantrum at a Vegas event and her run-in with Derek Jeter, pick up the new issue of Us Weekly -- on newsstands today!