Cycles of the Tongue

Have you noticed that sometimes almost all wines taste pretty good and then other times most wines taste uninspired or worse? It happens to me periodically, where I'll have a 1-2 week good or bad interval. It's especially annoying if I'm opening nice wines during a everything-tastes-bad interval. Due to bottle variation, I can't be sure if it was a bad bottle or just my taste buds being in a bad mood, so I keep right on opening the nice stuff, like I'm doing now.

I'm not sure what causes this, but I'm guessing a cold or illness might contribute to the bad intervals. And of course, the reason I'm writing this is I'm in a taste funk right now.