In the field of medicine, there is a practice known as ‘differential diagnosis’ which examines symptoms and looks at the variety of potential causes before suggesting a remedy or curative action. The classic example is one of headache, which can have innumerable potential causes, including tension or stress, indigestion, a variety of disease conditions, physical trauma, concussion, eye strain, etc. Depending on the underlying cause, a solution is then proposed and implemented.
Similarly, when physical fatigue overtakes the body, there can be a variety of different causes, and each one would have a different potential solution. We tend to overlook the causes by fixating on the symptoms alone. Yet there cannot be any true resolution without addresing the underlying cause.
Sri Aurobindo takes up the question of physical fatigue and outlines three major causes and the solution of each.
Sri Aurobindo notes: “Physical fatigue like this in the course of the sadhana may come from various reasons: 1. It may come from receiving more than the physical is ready to assimilate. The cure is then quiet rest in conscious immobility receiving the forces but not for any other purpose than the recuperation of the strength and energy. 2. It may be due to the passivity taking the form of inertia — inertia brings the consciousness down towards the ordinary physical level which is soon fatigued and prone to tamas. The cure here is to get back into the true consciousness and to rest there, not in inertia. 3. It may be due to mere overstrain of the body — not giving it enough sleep or repose. The body is the support of the yoga, but its energy is not inexhaustible and needs to be husbanded; it can be kept up by drawing on the universal vital Force but that reinforcement too has its limits. A certain moderation is needed even in the eagerness for progress — moderation, not indifference or indolence.”
Sri Aurobindo, Integral Yoga: Sri Aurobindo’s Teaching and Method of Practice, Chapter 10, Difficulties in Transforming the Nature, Weakness, Fatigue, Inertia, pp 309-311