Okay primary Fibromyalgia is when there is a catalyst like a car accident causes the issue. For example, a person gets whiplash and hurts themselves. The pain goes away then a few months later FM starts in. That is primary.
Secondary is when you have something like RA or spinal problems and then FM develops. They co-exist while the primary does not co-exist.
Let me share my experience.
I have primary FM. I have no reason for it, no car accident, no pre-existing condition. It just happened. I do have RA in my family and there are reports out there that if there is a family history for RA, then FM is a possibility as well. Aren't I lucky? I do have other health issues but the FM came first.
I hope that helps. I know its confusing.