Alternating Very low and high blood pressure

Hi I was wondering if sumone could give me some advice. I'm a 31 yr old female and have very low blood pressure and also bouts of high. I'm short of breath all the time. Had tons of heart tests with no real difintive anwsers. I'm couch-bound and unable to function. Lost 40 lbs, dizzy at times but the most troubling thing is feeling like someone is sitting on my chest. I just cant seem to feel like I'm getting enough air.

Had total workups and now Doc says Autonomic Dysfunction maybe or spinal issues. Any ideas??? Before I loos all hope for normality?