Try a glass of water with 1/4 teaspoon of sea salt in it, take this very soon after you wake up in the morning. If you feel better, it means your adrenal axis is off.
The symptoms you're describing either sound like postural hypotension or hypoglycemia, both of which I've seen improve upon treating the adrenals.
You are feeling better and performing better likely due to your time off. Nearly everyone takes these performance improvements as signs they can start training hard again...and they are mistaken most often, ending up right back in the same place they were before within a month.