Britney Spears has reportedly confessed to her rehab doctors that she has been bulemic since the age of 16. Spears allegedly told staff at Promises that she "pigs out" on bad food and makes herself sick in the hopes of losing weight. "Doctors are alarmed at the physical state she's in," said an alleged senior source at the rehab facility. "They confronted her about her desperately unhealthy lifestyle and the truth came pouring out." Spears managed to stop binging and purging while pregnant with sons Sean and Jayden but began again once she was ready to lose any extra weight she'd gained during pregnancy. "When she came here she was shaking and baking," said the insider. "Her whole body was wracked by spasms and she was hot one minute, then freezing the next." The combination of drugs, alcohol and an eating disorder had turned the popstar into a "human wreck," said the source. "Her first week in detox was real hell. She was in a total mess but slowly she's pulling through." Spears's condition has been improving since she was forced to admit her bulemia to doctors when they were trying to determine why treatment wasn't working. "For the first few days, she'd take her tablets, then go off and eat breakfast or lunch. She was throwing the whole lot up, so naturally her medications weren't working. Now the medical experts know why, her progress should pick up a little speed," said the source.