In a terrifying medical scare, Britney Spears suddenly collapsed while rehearsing – and a doctor was rushed to her side.

The pop tart was recently rehearsing new songs when she passed out as the dancers, as part of the routine, lifted her body while she lay sideways.

"She collapsed when the dancers went to put her back on her feet," revealed the source.

"She fell to the floor and landed on one of the dancer’s legs – and the dancer’s tennis shoe smacked Britney in the chest and on her face. It hit her chest with such a force that it caused a four-inch bruise."

Everyone rushed over to Britney, and they realized she had fainted. Her father Jamie ended the rehearsal and immediately called a doctor.

The 27-year-old singer suffers from low blood sugar – a condition her father Jamie has been trying to keep secret, divulged a source.

Although she’s physically strong, those close to Britney say she often doesn’t eat right or get enough rest.

Plus, she’s under a lot of stress from the tour.

"Her schedule has wreaked havoc on her body," the source divulged.

For the full story of Britney’s health problems pick up the new ENQUIRER.