Why does my vision go completely black for a few seconds?

[Dacoma]

My vision often becomes completely black for a few seconds. I don't know what caused this, can anyone explain this to me?

[Dacono]

If you get your black vision when you just stand up, it is more likely that you get low blood pressure or low blood sugar. However, you'd better go to see your doctor and have an exam.

[Dacula]

I often have such problem. It usually happens when I wake up or stand up suddenly. My doctor said it was because Low blood pressure or Low blood sugar. You may see the doctor to find the real cause.