We can conclude from the passage that when we feel fatigued …………

Our nerves are made up of cells, as is the rest of the body; and, like all cells, nerve cells must be nourished by the blood and will lose energy by activity. A period of rest usually restores nerve cells to normal. In the relaxed person, this can occur. In the person who is constantly under a degree of nervous tension, who has poor general health or is undergoing emotional disturbance, the cells are unable to regain their normal healthy condition. They live, instead, in a state of almost complete depletion, or fatigue. One result of this fatigue is a slowing down of impulses at the brain - a quicker loss of interest in what one is doing, the inability to stay at a task till it is done. It may become a complete lack of interest in anything. Not only mental but physical work tires the nerves as well. Work you're obliged to do but you don't like does this more quickly than work you enjoy. Such physical strains as tired eyes, a nagging headache, help tire the nervous system even if the part affected is not involved in the work one does. A change of work often gives a sense of rest because it brings different muscles into play.