Sometimes, when you close your eyes in the dark, you see what looks like sparks or flashes. Sometimes when you are tired, your vision seems to shift sideways and realign, like someone bumped into a camera, although you didn't move your eyes. It seems to me that some of these apparent sensations are not caused by (external) stimuli to the sensory apparatus but rather by an "overexcited" nervous system.
Is there a term for such "mistakes" of the visual system? I don't know what terms to use to describe these phenomena in scientific reports.