Madonna collapsed on stage twice at the weekend.

The 51-year-old pop star lost consciousness due to exhaustion on Saturday (August 29, 2009), but carried on with her performance at the Vasil Levski Stadium in Sofia, Bulgaria, despite her condition.

Madonna – who is on her "Stick and Sweet" world tour - first fainted during a rendition of her 1983 hit "Holiday," when her limp body was held up by backing dancers until she regained consciousness.

She passed out a second time and collapsed into a heap on the floor as she left the stage after "Spanish Lesson."

A source told Britain's The Sun newspaper: "Madge was really worried backstage. She had to sit down for a longer break than usual between songs."

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"She refused to end the show or take a break after the 'Holiday' dizzy spell. It turns out she's suffering from exhaustion."

Despite falling ill, Madonna has pressed ahead with her tour dates and played her penultimate performance at Hayarkon Park in Tel Aviv, Israel, last night (September, 1, 2009).

The source added: "She was advised to postpone the last two shows in Israel for a few days, but logistics and stubbornness stopped her. She'll do them then take some rest."

She is due to appear onstage at the Israeli venue again this evening (September 2, 2009) for the final concert of the tour.

Meanwhile, the singer's new single "Celebration" shows Madonna sporting a short platinum haircut as she snuggles up to her boyfriend, model Jesus Luz, 22, while her 12-year-old daughter Lourdes performs a back flip and joins in with backing dancers.