“I’m very brave generally,” he went on in a low voice: “only today I happen to have a headache.”

 — Tweedledum

My headache began on a Monday afternoon around three o’clock. The pain centered on my left temple and eye, constant, gnawing, broken only by sudden waves of sharper pain. My doctor was on vacation, but after several days I decided I couldn’t wait and took the next available appointment. By the time I made it to her office I could hardly walk across the room in a straight line.

The physician’s assistant was attentive, working down the neurological…