So it turns out there may be a medical explanation for this. I just had blood work done after I couldn't shake a cold and it turns out I have a pretty serious Vitamin D deficiency, that's been slowly getting worse for years.
It comes with a bunch of seemingly unrelated symptoms like: headache, extreme fatigue, temperature sensitivity, chronic pain, difficulty sleeping, getting sick often, etc...all things that make it hard to enjoy things as much as I used to. It's been pretty awful, but it makes sense.
Good news is that once diagnosed, it's pretty easy to treat. I should bounce back after a few months of supplements. We'll see.