AC, I do have something wrong with my eyes that causes me to get nauseated from certain types of movement (on the computer or on movies, etc. I can not ride in boats because of how the water moving against the way the boat is moving makes me sick......)
Anyway, I had paper taped across my screen for several days to hide the growl. Nice to take that off :D
My guess is that the swoopy notifications were inducing for some individuals the optokinetic reflex, a visual reflex that is in turn related to the vestibular (balance) system, thus causing a minor hallucination of movement. I concur that non-swoopy is much better.
Scarlet, I have something with my optokinetic reflex that causes my eyes to vibrate side to side quickly (Nystagmus ), for a few seconds when things like the growl fly across the screen....or if i focus on something that is little bitty in front of me. Thankfully my eyes do not do this all the time, only certain things trigger it (things moving in opposite directions like a boat on water, etc.) My eyes getting tired make it worse, that's for sure.
Minor hallucination of movement for me would be little dark things darting across the room out of the corner of my eye (that of course are not there). My daughter and mother have this, too. It is genetic.
Maybe it's because I use a laptop, but I never even noticed the growl messages swooped until people started complaining about it, and I didn't notice they stopped until right now, either. I guess I just never look at the bottom of my screen.