I keep getting faster. My regular 10km course takes me under 53 minutes consistently for a few months now, and recently it's far from unusual to do it in less than 52 minutes. Winter times last year used to be much closer to 60 minutes, consistently closer to 56 minutes. Why?
So if I go out and don't break any records or come in a minute or two slower than usual, I don't sweat it in the slightest. As long as all systems are functioning ok, it's all good.