I get these about 4 times a year, they last me about 20-40 minutes and 50% of the time end in a light headache. I can associate them with eye strain and lack of sleep.
First time I had one I almost shit my pants, now I just close my eyes and sit in the dark.
Here's an image of what I kinda see:
Hopefully your tests are all clear and this is all you are experiencing, minor annoyance really... unless your driving, then its time to pull over.