It sounds like you're 'blacking out' - that is, you're just about to pass out. When this happens to me, I get tunnel vision, leading to black spots in front of my eyes. If I'm lucky, I remain conscious, and my vision returns to normal.
But blacking out is definitely not normal. It can be brought on by any number of things - blood pressure, low blood sugar, etc. You'll need to be evaluated to find the cause.
sorry...can't help with that one...do you faint when this happens? Are you dizzy at the time? My vision gets so blurry at times...it seems like there is a film or something covering my eyes...but I haven't had any fading to black..
have you seen a Dr for this...you should see one asap...don't wait if you have problems with your eyes...OK....
maybe someone else will have some ideas...
take care
wobbly
undx