I've had these several times myself. For me, they start as a small "blind spot" at the center of my field of view, which was really scary, particularly if I was

I've had these several times myself. For me, they start as a small "blind spot" at the center of my field of view, which was really scary, particularly if I was trying to read or do screen-work at the time. After the first one, the appearance of the rainbow zig-zags was actually comforting, because that confirmed what it was. Since I was effectively incapacitated for the duration, I'd just lie down and enjoy the light show. It's been years since I had an occurrence, but the timing was pretty reliable. ~30 minutes: slowly growing blind spot at the center of my field of vision. ~15 minutes: rainbow zig-zags in a slowly expanding circle from the blind spot until it encircled my whole field of view, after which it faded out and I could focus pretty normally again. No headache during or after. After multiple rounds, I figured out the, or a, trigger: absinthe. Drinking absinthe reliably brought one on ~18 hours later. Only ever had one that I couldn't tie to absinthe. Stopped drinking absinthe years ago, and the scintillating scotoma stopped as well.