I've just had a really worrying 15 minutes. It started on the tube, as I was reading the paper. I noticed a weird flickering persistent light curving around at the edge of my vision, like I had been staring at the illuminated filament of a light bulb. It got brighter and brighter, obscuring my vision, so I had to look out of the right-hand side of my eyes in order to see anything. By the time I got to my station, it was so bad I could hardly see at all, and I felt nauseous. I worried that perhaps I was going blind, that I had glaucoma or something.

It was there in both eyes, which suggested - to me, anyway - that it was not a problem in the eye itself, but perhaps in the brain. I don't know why that should make me feel better, but it does. I tried calling my doctor, but couldn't get through.

Now I have a dull pain in my head, and the weird light thing is fading, but I still feel nauseous. Sounds like a classic migraine - something I've never had before. I shall call my doctor again in a couple of minutes.