A couple times a day, for no more than a couple seconds I seem to go blind. It does not happen as a result of a particular activity and there has been no recent head trauma. This has been going on for 2-3 months. My vision does not go blurry, it just literally goes away. No shadows, no light, nothing at all for 2-5 seconds then like a light switch it s back. My friends joke and say it s blinking, but my eyes are open when this happens. It is becoming more frequent and am getting very worried. What is this?