I black out randomly, not just when getting up but when I'm walking, working out, cooking, etc (thankfully never when driving, but I always worry about that...well that and the fact I'm a sun sneezer, yay tunnels and sudden bright light). Vision only, although I'll get a bit dizzy too, thankfully I have never fallen (knock on wood) but I just stop moving, and so far my vision has never been gone for more than about 30 seconds, norm only 5 or so. I get a large amount rushing of blood through my ears so voices are somewhat muted but I can hear them and answer (apparently it used to freak a few of my friends out when I would suddenly just stop moving and focus on nothing so I learned to just annouce what was happening and tell them to hold on a couple seconds).
So far no one has been able to tell me why but I've noticed it happens more often when I haven't eaten in a while (but not always) when I'm dehydrated (but not always) and when I'm hot (but not always), but it has happened when none of those things are involved. Some docs think it is blood pressure (but it's not that low) some think it might be some sort of visual epilepsy (but there isn't a common trigger) and others think it might be a middle or inner ear thing cause my ears will randomly ring. I'll prob never know for sure.
Def go check with your doctor, but if they can't think of anything be sure to pay attention to what was going on when it happened and if it happens again so you can figure out what to watch out for.