I haven’t had one in over a year knock on wood, but I used to get them just as described in the OP. It would usually start with what I thought was the after image from staring at something bright, like the sun reflecting off a car. Only it wouldn’t go away. Eventually it blocks out the center of my vision where I can only see what’s on the side and not what I’m trying to look at. Then it’ll move to the side and do some funky shimmering. That’s my warning to get somewhere safe.
My worse was once at work I got the aura, but couldn’t read or spell. Usually I could just work around it, trying to be mindful of my lack of vision. My worse ones have also come with feelings of nausia and stomach upset, but nothing really came of those feelings, thankfully.
The headache hasn’t been too bad in recent years, the worse will be the next day when I have what feels like a lingering hangover headache, where I won’t notice it unless I bend down, and then there’s a dull ache felt.
When I was working I figured it was caused by wearing my contact lenses through the night and into the next day. Also if I drank the previous night. Later they were because of no breakfast. I would get up and drink coffee and smoke unitl I got really hungry after noon sometime, that habit would cause them.
For recent ones I would just get somewhere safe and try to sleep, that would make me feel better. Unfortunately now I have this fear reaction as a result. If I know I’m engaging in behavior that used to cause one, if I see any after image in my eyes I get nervous and break out in a sweat. And that’s just with a legitimate after image, not a oncoming headache. It’s terrible to have that feeling and get so scared about it.