It could mean paranormal activity or just seeing things. It happens to us a lot.
I have seen a black figure in the shape of a person twice...what does this mean?
It happens to me frequently. I often see dark shadows in the shape of people or animals in my peripheral vision. I don't know why it happens and neither does my doctor. I've had it for many years.
Apparently it's harmless. Nothing has ever happened as a result.