Madonna’s final Sticky & Sweet concerts have been marked with worry doubt after she collapsed onstage midway through a show in the Bulgarian city of Sofia last Saturday night, The Sun claims.

The 51-year-old singer refused to stop the show and continued her rendition of “Holiday,” before reportedly walking off stage during “Spanish Lesson” after falling ill again.

A source tells The Sun, “Madonna was really worried backstage. She had to sit down for a longer break than usual between songs. She refused to end the show after the Holiday dizzy spell. It turns out she is suffering from exhaustion. She is anemic.”

The insider adds, “She was advised to postpone the last two shows for a few days, but logistics and stubbornness stopped her. She’ll do them and then take a rest.”