But. If you are past a certain threshold, ROS can do so much damage that it starts to affect cellular ATP production, leading to a tissue hypoxia. When this happens, it leads to onset of an acquired mitochondrial dysfunction. This is a pathological state that is characterized by a lingering fatigue as its main hallmark sign. Such fatigue does not go away after sleeping.
But usually it is not like 0 or 1. A person may have something in between and live without even knowing it, thinking that it's all just mental or age-related.
