Britney Spears is so stressed about her pop comeback her hair is allegedly falling out. The sexy singer - who took time off to marry husband Kevin Federline and have their baby son, Sean Preston - is said to be losing clumps of her luscious locks. Britney has even reportedly started wearing huge hats to cover her thinning tresses. A source said: "It looks like Britney is suffering from stress-related alopecia. But the real cause of her thinning hair is her constant fretting about getting slim and developing a new look for her return to pop.'' The singer - who gained 50lbs during pregnancy - has been feeling the strain because she has been worrying about her husband's partying, while caring for their baby, and is also concerned about getting in shape for her comeback.