The expression in Donguibogam that the spirit is unstable actually holds remarkably scientific insight when viewed through modern medicine. The phenomenon of repeatedly waking and failing to get deep sleep goes beyond simply lacking sleep; it is closely connected to complex operations within the brain and nervous system.
Our brain does not stop working even while we sleep, cycling alternately between REM sleep and non-REM sleep. Non-REM sleep is further divided from light sleep into deep sleep, and it is during this deep sleep that the body recovers, recharges energy, and strengthens immunity. However, individuals experiencing sleep maintenance insomnia face difficulty entering this deep non-REM sleep stage, or they wake easily at even minor stimuli despite falling into deep sleep. Just as Donguibogam describes the spirit failing to find its place and continuously shaking, the brain cannot fully switch into rest mode.
An imbalance of neurotransmitters significantly influences this phenomenon. Melatonin induces sleep, and gamma-aminobutyric acid calms brain activity; however, this balance breaks down if levels of the stress hormone cortisol become too high or if neurotransmitters like serotonin become deficient. The brain remains excessively in a state of arousal, or daytime stress and anxiety stimulate the amygdala, continuously sending alert signals even through the night. Irregular lifestyle habits, blue-light exposure from using smartphones before bed, and the intake of caffeine or alcohol also disrupt the sleep cycle, serving as primary causes that disturb deep sleep.
Furthermore, physical issues in modern individuals such as chronic inflammation, gastrointestinal troubles, and difficulty with blood glucose control also affect sleep quality. Poor gut health can hinder the production of sleep-related hormones like serotonin, and when blood glucose drops too low in the middle of the night, our body perceives it as a crisis situation and secretes cortisol, waking us up. In this way, the teaching of Donguibogam that sleep comes when qi and blood are in harmony reminds us once again of the importance of physical and physiological balance.
