I think I've found the source of my problem.
I ran out of allergy medication about a month ago. That was also the same time I ran out of cumin and switched to curry powder for my last batch of seasoning. I picked up a new bottle of generic Claritin on Friday ($7 for a 60-day supply) and the problem seems to have gone away.
Better living through chemistry, I guess. I probably should have bought a new jar of cumin, but I forgot. The curry is so tasty.