For the future readership I might add that I also have blood tests of cortisol, TSH and blood sugar. Every blood marker is absolutely normal.

Still feeling a little up and down, depending on sleep it seems, but feel sore thighs without doing sport, minor sore throat and headache in the pm most days. Since I've got nothing to go on apart from normal blood markers, I diagnose myself with overtraining that was worsened by catching a cold at the wrong time. Gonna give it a rest still, maybe some easy training, but probably it's better to just rest.