This happens to me too, though I'm not sure if it's happened while working out. It usually happens when I get up from sitting too fast, or after I whip my head back up after putting my hair in a towel post-shower. I've always had abnormally low blood pressure. You got me curious about it, so here's the wikipedia entry on it:
http://en.wikipedia.org/wiki/Phosphene
This happens to me too, though I'm not sure if it's happened while working out. It usually happens when I get up from sitting too fast, or after I whip my head back up after putting my hair in a towel post-shower. I've always had abnormally low blood pressure. You got me curious about it, so here's the wikipedia entry on it:
http://en.wikipedia.org/wiki/Phosphene