Spears, 27, who is currently on the North American leg of her 'The Circus: Starring Britney Spears' tour, is reportedly struggling with her energetic live dance routines, and was forced to leave the stage and vomit after becoming dizzy and nauseous.
"The choreography is insane - it's so fast it is really taking its toll on her," the Daily Telegraph quoted a source as telling the Mirror. "There is one move during 'Touch Of My Hand', where two guys dangle from the ceiling and pick her up upside down, which is really getting to her."
"She spins around for nearly five minutes some nights. The blood rushes to her head and when she gets down she complains of nausea and dizziness. There have been a couple of times when she ran off stage and vomited. She's asked if it can be changed," the source added.