I had this question posed to me recently as well so here is another page about why this condition happens!
Stress is the mainly the reason behind most illness that I know of. You could of course inherit it from your parents or grandparents so that is another reason.
It however can start after a car accident (whiplash injury).
So I hope the above helps!
Related articles
- Chronic Pain & Fibromyalgia (guardianlv.com)
info2uohyeah 