Officially, Miley Cyrus was rushed to the hospital because of a bad reaction to antibiotics, but TMZ says the real culprit is the singer's dog -- whose death sent her into a tailspin.

Miley, who just canceled a second show due to her hospitalization, has been in a bad way since her beloved Floyd died earlier this month, according to sources in her camp. One insider tells TMZ that she's been drinking and drugging heavily, saying, "She's been off the rails since this happened."

Miley tweeted an apology for the cancellation of Wednesday's show, saying "I'm not going 2 make it 2 St. Louis. I'm so sorry, but some things are outta my control."