I wonder why people see stars

I know why people see movie stars. And it seems clear enough why we
see celestial stars. But why we see stars when we stand up too
quickly, or of we jossle our noggin's seems like a total mystery to
me. It's not like they are simple phosphemes- instead they appear to
have a uniform color and move about. Although now that I think about
it, I can't be so certain that the movement doesn't come from the
movement of my own eye.

Perhaps people have explored this?
If so, I wonder how they induced people to see stars...