My doctor says:
The thing in my neck is called a
thyroglossal cyst. It's totally benign, won't do me any harm, and I can go in to see him at my leisure to talk about what we can do about it. He says it has nothing to do with my exhaustion.
I'm researching it right now, see what I can find out. I'm glad to finally know, and that it's not something more serious. Aah, sweet relief.