Hey, VAl
ME/CFS and FMS are similair but definately NOT the same thing, I have to beg to differ with your doctor. In fact there's a research paper out about just that. If you need the link, I'll message it to you.
In general, ME/CFS and FMS tend to have low blood pressure, but it is not exclusive.
I had very low blood pressure all my life and it shot up since 3 years ago after dental extraction surgeries.
Sometimes, bp can be hereditary too regardless.