Hi Cheechg....Yes, you like everyone else who has low BP wants to know "why", so maybe we can actually treat the underlying cause, like Addison's disease, or???
Unfortunately, I don't think that will happen in our lifetimes; I've been asking my cardiologist for several years, now, and she has no answer! So, we end up treating the symptoms, which is better than no treatment, but very frustrating. I mentioned my low BP to my vascular surgeon (because I knew he was very intelligent; a member of Mensa, and to my surprise said "yes" he would suggest some tests, which I've just completed and will see him in a few weeks for a follow-up visit. He also will be giving me a referral to another cardiologist for a second opinion. Like he said, don't expect a miracle, but at least he's trying; something none of my previous cardiologist's have done, so I'm very happy to have met a doctor like him! I know this is probably not the answer you're hoping to hear; to treat your symptom, simply add table salt (NaCl) and your BP will go up.