I Think What I Have Is Low Blood Pressure. After

I think what I have is low blood pressure. After I stand, after a few minutes, if I am still standing, as standing in line, I feel faint. I was in line for an hour last night 5-6 p.m. and felt faint the entire time. No blackness, my head feels odd, light headed, hands were sweaty, I was not hungry. I had a hearty lunch at noon and a handful of nuts 1 hour prior.
Other times it feels like an anxiety attack where there's a moment of chest pressure, instant acid reflux, and odd feeling for minutes following. What is this?