From the perspective of modern medicine, the heart heat described in Donguibogam is remarkably similar to sympathetic nervous system hyperactivity. That feeling on sleepless nights when your mind is racing and your heart feels like it is pounding stems from your body continuously sensing a threat and remaining locked in fight-or-flight mode.
At night, even when you are lying in bed, your brain still assumes it is daytime and prepares for emergencies. This is deeply linked to chronic hypothalamic-pituitary-adrenal axis dysfunction. When stress persists, the hypothalamic-pituitary-adrenal axis becomes hyperactivated, keeping the secretion of the stress hormone cortisol elevated even at night. Cortisol is normally secreted in the morning to wake us up and provide vitality; when it remains high into the night, it interferes with the secretion of the sleep-inducing hormone melatonin and keeps the brain in a state of arousal.
Furthermore, an imbalance in intracerebral neurotransmitters plays a major role. A state of heart heat can be viewed as an agitated condition, akin to the brain consuming an excess of caffeine. Levels of norepinephrine and dopamine, which induce arousal, are excessively elevated, while the functions of serotonin and gamma-aminobutyric acid, which induce sleep and alleviate anxiety, are frequently suppressed. In particular, excessive thinking is a phenomenon where the brain's frontal lobe becomes hyperactive throughout the night; the frontal lobe, responsible for rational thought and problem-solving, cannot rest even for a moment, continuously regretting the past and worrying about the future in a loop of rumination.
In this state, stage 3 non-REM sleep, which is responsible for deep sleep, decreases, and the frequency of brief awakenings increases, causing sleep quality to decline markedly. Shallow sleep is evidence that the brain has failed to rest and recover sufficiently. Over the long term, this can lead to decreased immunity, chronic fatigue, impaired concentration, and even depressive feelings or anxiety disorder, so it must be recognized not simply as trouble sleeping, but as a warning signal threatening the health of our entire body. Donguibogam's concept of heart heat goes beyond merely a hot chest; it encompasses a comprehensive problem where complex imbalances throughout the brain, nervous system, and hormone systems disrupt the vital life process of sleep.
