Why do I have feel terrible the next day?

I need advice. I had a great workout yesterday….. a big one…. and felt great after. Went to bed and now today, I feel groggy. I didn’t eat much or hydrate after the workout and today I had dark pee. What can I do? I want to do another workout today but i’m not feeling good about it.
Why do I have feel terrible the next day?
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