Forced to cancel performances at festivals in four European cities, Allen showed fans that she really is too ill to perform by posting a photo of her holding up a doctor's letter on her MySpace page.
"Hello everybody, I've have literally been around the whole world in two weeks from London to Japan around Australia and then to L.A. and Vegas then back to L.A. for a 17 hour video shoot," she writes. "And now I'm back in London eating my mum's chicken soup 'cause I'm afraid the travelling has caught up with me."
Suffering from both throat and nose infections, the 22-year-old "Smile" singer decided to take the unusual step to thwart potential critics.
"I've got sinusitis and strep throat – I don't even know what that is – and have been advised to take a couple of weeks off by a doctor in L.A. and a doctor here," she says.
The sick note – valid until Aug. 17 – was issued in Islington, north London, and Allen uses it to explain why she decided to pull out of the shows.
"Before anyone starts trying to accuse me of neglecting my fans I want to apologize and say how sorry I am, but I can't risk causing any permanent damage," she says. "I hope people can understand and aren't too angry."
Allen may have to contend with upset American fans too after immigration officials unexpectedly revoked her U.S. working visa. Hopefully, she can get a new one by next month when she is expected to tour here.