The singer made the announcement on Twitter where she also said the illness features in her latest documentary.
Fibromyalgia is described by the National Fibromyalgia & Chronic Pain Association as "a common and complex chronic pain disorder that causes widespread pain and tenderness to touch that may occur body wide or migrate over the body".
Lady Gaga's romantic life seemed to be all wrapped up when she announced in February 2015 that she and actor Taylor Kinney were engaged.
One fan wrote: "It's incredible how just this one tweet has created a discussion about fibromyalgia and chronic pain and is allowing many to open up.' To which Gaga replied that she's "praying" more people open up about it so 'we can help each other".
In many cases, the condition appears to be triggered by a physically or emotionally stressful event.
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"I sold 10 million [records] and lost Matt [her ex]". I sold 30 million and lost Luke.
She also goes on to share her experiences with treating the symptoms, and was subsequently inundated with messages of praise from fans who also struggle with their day to day lives because of chronic pain. "This is the third time I've had my heart broken like this".
Unfortunately, there is no current cure for the disorder and only pain management is available.
In between writing songs and dealing with chronic pain from a hip injury, Gaga also discusses Madonna's "reductive" shade towards her.
Back in 2016, she posted an Instagram explaining how she deals with the pain, though she still had not revealed what her particular illness was.