Sight goes black for split second when waking up.

I have experienced it 6 times so far over the course of 5 months. I wake up in the morning and before I open my eyes for a split second I only see pure black. I thought the first couple of times I was not awake but now it did it twice within 5 seconds of each other. I screwed my eyes up to see if everything would go black but of course it was daylight in the morning so it was impossible to make it happen. It happens so fast and I have no idea what could be causing it. Anyone experience anything similar or have an answer? It only happens upon waking up in the morning.