I have neurally mediated hypotension, which causes the BP to drop. I too failed the tilt table. It is a natural response for your heart rate to increase in order to compensate for the low BP. This 'might' be why your HR is high while your BP stays low. I take both florinef and midodrine along with a high sodium diet. It's not perfect but I can function, drive, etc.

Autonomic dysfunction is a form of neuropathy and can have many causes. Mine is caused by the autoimmune disease, Sjogren's. In many cases, autonomic dysfunction not limited to just tachy rates & BP. Mine also involves other heart rates/rhythms, temperature regulation, gastric motility, balance, and even vascular spasms. The treatment is specific to the effected system. Treating the underlining disorder (if you know) can help the autonomic dysfunction. Have you been worked up for causes of this? If so, what tests?

I would contact your doctor about finding a better combination of meds so you can function more normally.