This is called motion parallax, and it occurs because objects viewed at different distances move across the retina at different speeds. “Our brains rely on motion parallax cues as well as cues from ...

Motion Parallax: The relative movement of objects at different distances, resulting from the observer's own motion, which provides cues to depth.

Specifically, discomfort was due to a specific sensory cue called motion parallax, which is defined as the relative movement of different parts of the environment.