"I feel bad because I haven't been able to say anything to the fans to let them no [sic] why I've been absent," Lavigne wrote. "I'm torn as I'm quite private� I'm not feeling well. I'm having some health issues. So please keep me in your prayers."

Now the cause of Lavigne's illness has been revealed in the latest issue of People, which the pop-punk singer covers. It turns out that she has been battling Lyme disease.

Lavigne found out her diagnosis after her 30th birthday trip to Las Vegas last September. "I could barely eat, and when we went to the pool, I had to leave and go lie in bed," she said. "My friends asked, 'What's wrong?' I didn't know."