Hello,
For syncope/fainting to occur, either the reticular activating system in the brain needs to lose its blood supply, or both hemispheres of the brain need to be deprived
of blood, oxygen, or glucose. Since most
of the
causes have been ruled out, it can be due to blockage of arteries supplying blood to the brain esp. the carotids or vasovagal attacks. Other than that, Hypotension, Anemia, Dehydration and Hypoglycemia also need to be ruled out. Fibromyalgia does not cause syncope attacks.