My migraines are mostly of the "silent" variety (blind-spots, visual disturbance, scintillating scotoma, confusion, aphasia), sometimes there's significant pain, often not. There seems to be some connection between the migraines and ME/CFS (my collapse was precdeded by several months of increased migraine severity and frequency), but there is a strong distinction between the more acute elements of each. Even where symptoms overlap, the migraines follow a definite and consistent progression, whereas PEM seems to go up and down and come and go (to say nothing of the different durations). That said, you're absolutely right that some of vestibular symptoms, the particular nature of the motion-sickness/nausea, and sensory sensitivities can all feel very, very similar - including both the exacerbated forms that arrive with PEM and the constant forms that never really leave.
Some of the cognitive difficulties can be pretty close as well, though they are excrutiatingly difficult to describe.
