Low Blood Volume
There is a great article on this site about mitral valve prolapse that talks about low blood volume. I realized that I'm not drinking enough water. People with MVP sometimes aren't thirsty and consequently don't drink what they should. And then you get the resulting symptoms, including tiredness and low blood pressure.
"Dr. Watkins tells patients to drink eight to ten glasses of water a day and get more salt, which makes the body hold onto water. (You don't need to worry about driving up your blood pressure too high since it's already so low to begin with.) He also instructs them to cut out caffeine, which stimulates adrenaline production and prevents the body from hanging on to water, and to exercise, which keeps heart rate and blood pressure in check. If these lifestyle measures aren't enough, he moves on to one of two medicinal remedies: a beta-blocker, which curbs the response to adrenaline, or fludrocortisone, a drug that has the same water-conserving effect as salt, only more so."
The other thing I think I have done is cut my magnesium. Magnesium deficiencies are common in people with MVP.
I had cut out some calcium supplements and forgot that it would also cut my magnesium. And I also cut my salt intake. If you have very low blood pressure you should keep your salt intake at normal to high levels. If you limit salt your blood pressure will fall even further. So I think I haved basically sabotaged myself. No wonder I'm tired all the time. We'll see what my doctor says.
