Once I had a dream that started fading so I tried to stare at something to see if it would become clearer. It made me blind instead and I woke up shortly after. It wasn't like pure blackness though, it was more like something blocking my vision.

Two other times I went through a mirror it was all black and nothing around me at all. That time I don't think I was blind but that there was nothing there and I was in empty space.