Occasionally see black on the right side or loss of vision?

Hey friends,

I've been having vision problems in my right eye for some time now. It's as if my vision goes blank for a second, or my eye goes black for a moment, and then everything goes back to normal. It occurs most often after I stand up or when I move my head down or to the side. It doesn't happen every day, but it does happen occasionally. Has anyone experienced something similar or perhaps knows what might be causing it? I've already been to the ophthalmologist, but they didn't find anything suspicious.

If anyone has any idea, please reply.

Thank you in advance!