Fibromyalgia, a widely misunderstood illness, confuses and frustrates both patients and doctors alike. I know because I’ve seen it from both sides—as both a physician and a woman with the illness myself.

This common chronic disease is characterized by widespread muscle pain, fatigue, and brain fog. It’s estimated that 5 million Americans currently suffer from the disorder, and close to 90 percent of those diagnosed are women.

Still, there remains a lot of confusion about what the illness really is and how it’s treated. Here are five truths about fibromyalgia that are not widely known, even by most doctors: