Britney Spears has reportedly been throwing tantrums and locking herself in a room during nervous attacks so bad that her father has to call the doctor, The Telegraph reports. The 27-year-old pop icon is preparing for a world tour, but one source said it's in danger of not happening because Britney "fears her performance will be branded a flop." The world tour is slated to begin next month. Britney's two sons, Sean Preston and Jayden James, will travel with her. Earlier this week Osama "Sam" Lufti, Britney's former manager, sued her for libel, defamation, battery, intentional infliction of emotional distress and breach of contract.