The dots are white blood cells moving in the capillaries in front of the retina of the eye.

From the wiki page.

So, yeah, it makes sense that very similar or even just the same effect can be intensified by all those things you mention, they all alter the motion of blood in your eyes.

As to a big chunk moving?

I am not an eye expert, but I would intuitively think that yes, a big splotch moving could be the retina itself moving… but it could also potentially be something like a clot in one of those capillaries breaking loose… which is probably still bad, but maybe not necessarily as bad?