Lady Gaga cancelled an Indiana concert appearance last night (Jan. 14) after collapsing backstage due to exhaustion and dehydration. "An hour before the show I was feeling dizzy and having trouble breathing," she posted on Twitter. Paramedics diagnosed her with an irregular heartbeat, she said. The performance, at Purdue University in West Lafayette, Ind., has been rescheduled for Jan. 26.

Lady Gaga is in the midst of her national "Monster Ball" tour which began Nov. 27 in Montreal. The next scheduled date is tomorrow (Jan. 16) in Atlantic City, then two dates in Connecticut and four shows at New York's Radio City Music Hall next week are all the remains of the North American leg of the tour. A three month run of European dates begins Feb. 18 in the U.K.

"I am so devastated," she later posted on Twitter. "I have performed with the flu, a cold, strep throat: I would never cancel a show just based on discomfort.

"I hope you can forgive me. I love my little monsters more than anything, you are everything to me."