They always happen when I stand up, especially when I've been sitting down for long periods of time watching TV, reading, etc. My vision gets blurry, blacks out, and then returns with pretty little spots before correcting. All of it happens in about 5 seconds.
I'm very healthy, and rarely get sick except in flu season. I haven't thought to mention them to a doctor because they don't really bother me too much, so I never think about it during a checkup.
What could be the cause? Is it be just a rush of blood circulation?