I figured it out! No, I don’t have a baby chest-burster lost in my skull (thanks, Michelle, for the image – that’ll linger). I rode today, and when I ride, I wear a helmet. When I wear a helmet, I put my hair in a ponytail, and the helmet goes on over the base of the ponytail. Some days I don’t get the placement just right, and midway through my lesson I become aware of this painful pressure in one spot near the base of my skull. I forget about it as soon as I take the helmet off, relieving the pressure, but apparently that 45 minutes or so of pressure leaves a lasting sensitive spot. That must have happened last Friday. I don’t remember that specifically, but I definitely remember that pain from other lessons, so I’m willing to go with this theory. My odds of survival are better with this theory.
I got the placement of my ponytail right today – no pain, no fear of aliens. Well, no pain.