Training in general puts a strain on CNS. Maybe take some additional Vitamin B-6 if you’re concerned. And make sure you get lots of rest and eat lots of good foods – although you should be doing that anyway.
I think the training quality thing is largely psychological. I, too, have experienced much better workouts while sick than I did the week before when I was healthy.
Nowadays I prefer to conserve my strength to completely fight off illness before returning to training – especially with all of these “mutated” viruses apparently going around.
