Depression is not merely a mental disorder involving feelings of sadness, but rather a systemic condition that produces widespread effects throughout the entire body. When depressive feelings deepen, the body often feels heavy as lead and fatigues easily, frequently accompanied by muscle pain or chronic fatigue. This occurs because the brain and body are intricately linked.
First, depression disrupts the brain's neurotransmitter system. Imbalances develop among key neurotransmitters, such as serotonin, which influences feelings of happiness; dopamine, which relates to motivation; and norepinephrine, which regulates energy. These compounds do not simply alter mood; they play critical roles in regulating energy metabolism, sleep, pain perception, and muscle activation. A deficiency in these compounds naturally leads to lethargy, impaired concentration, and chronic physical fatigue.
Second, depression leads to hyperactivation of the hypothalamic-pituitary-adrenal axis, the body's primary stress response system. Prolonged overproduction of the stress hormone cortisol accelerates muscle protein breakdown and inhibits new muscle formation. Cortisol also increases inflammatory responses, and chronic inflammation causes muscle fatigue and pain while impairing recovery. It functions much like an overheated engine wearing down its mechanical components prematurely.
Third, chronic depression and stress produce autonomic nervous system imbalance. When the sympathetic nerve becomes excessively active, the body remains in a persistent fight-or-flight state, unnecessarily consuming energy. This reduces sleep quality, impairs digestive function to hinder nutrient absorption, and ultimately degrades the body's capacity to produce and store energy efficiently. What the Donguibogam describes as spleen-stomach dysfunction corresponds in modern medicine to reduced digestive absorption and an imbalance in energy metabolism.
In short, depression disrupts energy production and utilization by destabilizing neurotransmitters, elevating stress hormones, and disturbing the autonomic nervous system. By impairing muscle function and recovery, it brings on systemic lethargy and physical fatigue. It is akin to an illness of the mind taking away the body's physical energy.
