For sleuthing this sort of HR problem, I rely on taking my morning resting and standing-resting HRs. In your case, probably too late, you would have had to have been doing that long enough to establish a baseline and have seen how it varied with training inputs. What happens in overtraining is that exercising HR w/r to effort drops and morning resting HR increases. I'd see a rise of say 4 beats in MRHR and would back it off for a day or two, see what happened to my MRHR. A rise of 6 beats would mean back it way off for at least a week or until it came back down. I don't know if you have any data for that, but it's worth a look or a check.