On Friday I had my doctor take some blood tests. It turns out my marrow iron level is low. That explains why I'm so wiped. He said it's probably because I donate so often (I didn't realize there's a downside to donation), but if I take an iron supplement for a month or two I'll be back to normal. I envision large leafy green salads and (cross my fingers) steak in my future.
Ah, it all makes sense now. Goldy is the puppet master!