I have chronic low blood pressure so get light-headed a lot and have to bend over for awhile after standing up on a regular basis, or that starts happening... But because I know of that and how to fix it, I've never actually fainted. Closest I came was once when I was getting blood drawn for some labwork and not only was I dehydrated, but they had a new person doing it and they blew a vein in one of my arms. So the experienced tech tried in my other arm, and I closed my eyes, and suddenly she goes "Whoa. Uh, okay, take some deep breaths" and I had no idea why she sounded alarmed, so I opened my eyes and everything looked like a staticy television set. Oops. Took me about half an hour to feel normal enough again that I could drive myself home from the lab. :P