For me it starts with a small patch of my visual field going blind - not white or black, just not able to see anything or make out detail in that area. Typicall

For me it starts with a small patch of my visual field going blind - not white or black, just not able to see anything or make out detail in that area. Typically it's a spot in the center of my vision such that I can't read. After 5-10 minutes, flashing, swirling colored patterns will appear in that same spot. The affected area then enlarges progressively over the course of anywhere between 30 minutes and several hours, covering a polygonally shaped area with the flashing swirling patterns. Sometimes it will stop after 2-3 hours and gradually disappear. Other times the area of blindness and flashing colors will continue to expand for 6 or more hours until it covers an entire half of my visual field. After the visual aura disappears, usually (but not always) an intense headache will start that lasts the rest of the day. Triggers for me are unknown but in the past have included air pollution (e.g. smoke from wildfires) and very bright light (watching a video with a white background for too long on a high brightness TV). I have also noticed greatly reduced frequency of these migraines after I started taking magnesium glycinate daily.