This afternoon, I was reading something on the computer screen, when I realized I could not see a spot about the size of one letter in the center of the screen. Instead of the letter I was trying to read I saw a spot of roiling light. I stopped reading and looked around and the roiling light spot was getting larger and opening up into an arc, a backwards c, that glittered and took on a zigzag shape and moved gradually off to the right. It looked the same if I closed one eye or another, signifying that nothing was wrong with an eye, but that my brain had to be the problem. I did not, however become alarmed. I had read Oliver Sacks's book "Migraine" and knew about the pre-migraine visual disturbance called "scotoma." I googled "scotoma," went to the second item Google retrieved, and found this, an animation of "a classic migrainous scintillating scotoma from a small paracentral bright spot to an enlarging bright, curved, zig-zag line (the scintillation)." The animation was precisely what I saw--save that mine exited stage right instead of stage left. The website predicted it would last 10 to 20 minutes, and in fact that was exactly so: the arc slipped out through my peripheral vision.
That was, for me, the all-time best performance by the internet. But yes, I did still call the doctor, mostly because it happened again a half hour later. I got sent to the emergency room, where I told the story of my scotoma to five different people, with the final verdict coming from the neurologist who said, given that I never did get a migraine headache out of all of this, that it was a "migraine equivalent."