> I assume that eg. when exercising too much etc., even a healthy person would get a hypoglycemia?

I doubt so. I tried water-fasting for a week while exercising a lot and felt great. Fatigue from jogging felt nonexistent as compared to normal (my normal endurance is pretty low). Resistance exercise muscle fatigue felt way stronger (low recovery rate) than normal yet apparently didn't affect the brain as I neither felt sleepy, nor moody nor intellectually impaired.