Might be a bit off topic, but I think it's interesting enough to say it here.
One day I was sleeping and dreaming, and in my dream I thought "what if I'm dreaming?" and tried to open my eyes. I indeed opened them in reality, but:
1. I was paralyzed, because even though I was conscious my sleep paralysis did not have time to go off, and
2. While I could clearly see my room, some things were different, kind of like overlayed images of similar shape. For instance, where there was a chair with a coat hanged on it, I saw a very big floating face. Or, where was the side of my library, there was a man standing still. It was not like changed images, more like images on a layer above the real ones (if you ever used photoshop, you know what I mean).
In a few minutes, the additional images faded off, and I could move again.
This is because of how we actually see. We think we see solid images, but what we actually see with our eyes is a multi-colored blur. Our ming fills the gaps using its experience to understand what's what in that blur, using a special memory called Optical Memory. So most of what we see is in our minds. That also means that if our minds are tired, dreaming or overworked, they can interpret things the wrong way, and information from normal memory or/and imagination can be added to our optical input. Simply put, our mind can play some really odd optical tricks.
Just thought it would be interesting to say this. Sorry for the off-topic.