Funny you should ask that... lol. Because, for years, this has plagued me. Then my husband bought a blood pressure machine to test his own hypertension, and when I took mine, it was on the low side. So I figured that maybe (hopefully) that's the problem. (That would be good news).
That's probably it... I have naturally low blood pressure, too, and I sometimes black out like that. No worries... for now! ;-)