Livets Bog, vol. 2
Tiredness is the same as microscopic sensations of pain.
336. As the animal-like existence of terrestrial man is so largely promoted by explosive energies, naturally a great destructive process follows in their wake. It is not merely the murdering and destruction of the bodies of fellow beings, but also the destruction taking place in the corporeal body of the individual himself. The explosive energy causes an immeasurable wear and tear on the nerves which again, in greater or lesser degree, weakens or paralyses the individual's manifestation of consciousness and well-being. This weakening or paralysing effect is known in daily life as "tiredness". In reality this "tiredness" is the result of a number of tiny microscopic injuries in the very nerve-tissue; they are wounds and sores in the "flesh" of such nerves. As the injuries are so microscopic, the pain is also microscopic and it is this, their microscopic nature, which makes us experience these pains as just "tiredness". So "tiredness" constitutes simply microscopic sensations of pain.