FORMER teen idol DAVID CASSIDY suffered a humiliating meltdown on stage, sparking fears that he could land back in rehab.

The 62-year-old star of the hit 1970s sitcom “The Partridge Family” completely lost it July 1 at the South Point Hotel and Casino in Las Vegas, The ENQUIRER has learned. Cassidy, who was busted for DUI in 2010 and spent time in rehab fighting his addiction to booze, forgot the words to songs, scolded the audience and even told fans to shut up, say sources.

“David was clearly behaving like he was drunk out of his mind or high on something,” an insider told The ENQUIRER.

“The concert was supposed to be a loving tribute to Davy Jones of The Monkees, who passed away in February.

But people began  booing, and at one point David started playing drums and lost one of the drumsticks. Then he started rambling to the crowd about fall­ing off the drum chair during a previ­ous perfor­mance.”

Cassidy’s publicist Jo-Ann Geffen claims the entertainer “was not feeling well and made the mistake of combining cold medication, which he needed for his voice, and cortisone for eczema.”

About 60 people stormed out of the singer’s atrocious performance and demanded refunds. A regretful Cassidy hopes to make amends with a free concert for charity, but the talent booker vows he’ll never be invited back to the hotel-casino.

“David was an embar­rassing mess,” said the insider. “We just hope he gets the help he needs before it’s too late.”