Yeah. Had the same thing when I was a kid. But outgrew it as I get older. Vision will black-out for few seconds upon sudden change of position like from sitting to standing up. Something to do with blood pressure as mentioned by Nancy. Anyway take the advise of the expert here.
Look up "orthostatic hypotension" and see if that sounds familiar. It just means low blood pressure upon standing up. Definitely see your doctor about it.
That could be heart problems also. See your eye MD and your family GP/FP.
JCH MD