Fear of not being intelligent anymore; fluffy summer brain

Last night at dog class, the instructor put a piece of duct tape on the carpet in front of each dog and said we were to start teaching the dog to touch it with a paw. I couldn't figure out how to get Buddha to know what it was that I wanted of him. It turns out that it was a "challenge" and we were supposed to be creative in our response to it. One way, if your dog already knows how to shake, is to pick up the piece of tape in your hand, say shake, and click and reward the dog for touching the tape in your hand. Honestly, that never occurred to me. I felt this chilly feeling in the pit of my stomach. Not the for the first time lately, I wondered if I am less intelligent than I used to be, less creative. There's a bit in Dorothy L. Sayers' Gaudy Night when a character dismisses another character by saying she had one of those fluffy, summer brains that flower early and go to seed. I wonder if I had a summer brain, too, and now I've gone to seed. I wonder if all of the anguish and failures of the last few years have knocked the intelligence out of me? I know it's been a long time since I've NOT woken up tired, is that part of it?