It would start with a shimmering pattern obstructing my vision where the bright light was, which would grow into a c shape and get bigger until it surrounded my vision and then faded away. About 15 min after the shimmering pattern faded the blistering pain would start and last for about 5 hours, with lingering light sensitivity until the next day.
I later realized that something about a rapid change in brightness (from dark to bright) would trigger them for me.
Another time was triggered by a high school shop teacher lighting a welding torch.
The best way to relieve the pain I found was to turn out all the lights and dunk my head in cold water, which I discovered eventually in desperation for relief.
I would only get them every few months, but when I did I would be pretty useless for most of the day. I stopped getting them in my early 20s. No idea why, but I am grateful. They sucked!