Hypothesis: The nasal fatigue reflex

Natural selection results in adaptations. I suggest that unexplained fatigue may be an adaptive response to nasal impairment. For macrosmatic animals, intact olfaction is necessary to detect predators. In such animals, any reflex (e.g., fatigue) triggered by nasal dysfunction that limited exposure would offer great survival advantage. The “fatigued” animal would remain in its protected environment, unexposed to hungry carnivores, while the nose healed. In humans, clinical syndromes associated with unexplained fatigue (chronic fatigue syndrome, tension fatigue syndrome, allergic fatigue, neurasthenia, etc.) are characterized by symptoms that, in part, are nasal in origin. The older medical literature does describe the resolution of fatigue in neurasthenia after nasal treatments. Nasal reflexes in animals do cause significant systemic effects, including an inhibition of muscle action potentials that is, perhaps, analogous to the “heavy-limbed” sensation of those with fatigue.