One thing you should know first is that every case of Fibro varies. One person might have all of the tender point and just experience overall pain, and another person might fall short of the required tender points and mainly feel pain in their lower body. It all depends on the person.
The most current things I have read on FMS talk a lot about the central nervous system and how it has basically gone amuck. My rheumy said that fibro sufferers brain scans actually differ from healthy people. Certain parts of the brain are more sensitive/more active than they should be.
The other arguement is that it is an immune dysfunction. Some believe that people with FMS have disturbed immune systems and the concentration should not be on giving pain meds, but on getting the immune system healthy.
Sickness can trigger FMS. If you have had a major illness, accident, emotional stress, etc in your life coinsiding with the onset of your symptoms, then it is very possible that you have FMS.
FMS sufferers don't have a low pain threshold, or maybe I just don't like the way that sounds. Our nervous systems are just oversensitive to many different things. I believe that women naturally have a high pain tolenance...I mean we are designed to give birth (and that's no walk in the park).
From personal experience, I heal more slowly after surgery. I take longer to recover. I often have complications (not life threatening or anything like that), but on at least one occassion every doctor I have seen has been a little puzzled by what my body does.
I hope this helped a little. If someone sees something in here that is wrong or can explain it better, then please correct me. I don't want to add more confusion to a person who is already confused.