Several decades ago people started reporting seeing things that weren’t there. Or rather scientists started to note that some people who reported seeing things that others couldn’t were starting to agree with each other in surprising detail. Sure there have always been trends such as alien watchers agreeing on broad details, but these were very specific details. Sightings of a particular type of six leaved plant growing in helices under damp bridges. Or seeing new breeds of rabbits with unusual fur patterns. Mundane things from otherwise normal people that only drew attention because of the fact that no one else saw them.
The sightings varied by region and time as would expected of animals and planets in different climates around the world, but the most striking and exotic thing was that everyone afflicted reported seeing auroras on otherwise clear nights. And thus in the popular parlance the affliction became known as Aurora Syndrome.
There was a bit of a media fuss, but since most of these people were otherwise completely sane they were soon released. And being sane most of them kept quiet about future sightings to blend in. In the short excitement tuned news cycle of modern life, this wasn't much of a story, so Aurora Syndrome faded into the background. It became something children were diagnosed with early in their lives and learned to keep to themselves or only talk about with others that had the syndrome.