> About 15 minutes before the shimmering happens, I can already feel that something is off with my vision. I've had only a couple of these in my life, both bro

> About 15 minutes before the shimmering happens, I can already feel that something is off with my vision. I've had only a couple of these in my life, both brought on by stress. For me they've both been preceded by about 15 minutes of a "feeling of impending doom" (which apparently is an actual medical symptom).