You know, I went through something like that too. I was completely lethargic, no matter how many hours I slept. My doctor thought maybe it was my thyroid, maybe it was my diet, maybe it was caffeine crash. Turns out, it was depression. Once I nipped that in the bud, I'm so much better now. Physically and mentally. I hope you can find the culprit and solve it, and just feel better.