So that’s what it was! (Just googled it)
I had one of these about 1.5yrs ago driving back from a stressfull welding job. Started as a small blob just out of centre vision & grew substantialy larger over 5 mins or so , kalidescopey diamond type sparkles round the edges of the hazey blob. Luckily I was passing a hospital & pulled in as I thought I was having a stroke!
I pat my shants big time when my vision started blacking out , by the time I was seen to it had cleared & occular migrane was mentioned , but I never looked it up for fear of a terminal google diagnosis : )
Often wondered if it was a T.I.A , another mystery solved by the STW colective.