Yes, you described it perfectly. I’m sorry you had to deal with it, but it is reassuring to know that other people experienced this and that you can heal from it. Yep, I believe mine stems from heavy weightlifting. I pushed crazy hard - to the point to where I would get chills mid-workout. No good.Damn this describes how I felt for years and years. Every morning I would wake up and feel this "sick fatigue", malaise, nausea or hungover feeling. Not really tired, but kind of like I had been poisoned by something (stress?). It was awful! I think you are definitely on to something about the link between "sick fatigue" and poor digestion -- since I worked on improving my digestion (had to eliminate gluten), and taking measures to eradicate H pylori, I don't wake up feeling poisoned or hungover any longer. Oh and I had a very similar background to you where I pushed myself with heavy weights, despite my body telling me not to, until I physically couldn't any longer. Had to stop working out completely for years. Only recently have I been able to do some light bodyweight stuff again without my sleep suffering or feeling poisoned when I wake up.
My only advice would be to relax and not push the envelope so much with exercise, including light exercise like walking or jogging, even if you feel a little better on a particular day. For me I really had to exercise restraint to not overdo and "break the energy budget", that was what allowed me to get better in the long run.
I think you’re right about the resting. I need to dial back even more and recover. Maybe some light stretching and slow walking just to keep the blood moving (I don’t like sitting for a long time, my feet get clammy and cold). The other day when I tried a brisk 30 min walk then did some bike throughout the day it may have thrown off my sleep.