I cannot speak to your current state of health, but my acupuncturist has detected a weak pulse at times. I have POTS and experience a lot of brain fog, fatigue, and sometimes chest tightness as well. The chest tightness can be really unnerving. It can be very frustrating having to wait so long to get a proper diagnosis and the find the right medications to treat it. I hope you are able to see a specialist soon to help you with this. I remember being very scared as well before I received my diagnosis.
With regards to your blood sugar, I do recall that you mentioned that you had transitioned to a vegetarian diet. The only advice I have to offer is; try to eat whole foods and not too many refined carbohydrates (don't overload on the carbohydrates- eat plenty of vegetables -if well tolerated). Starting a new diet often requires a lot of research.
I hope you get some answers soon.