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Xuan (dizziness/blurred vision) means confusion or disorientation. It is composed of "Mu" (eye) and "Xuan" (dark/mysterious). "Xuan" implies darkness, referring to the sensation of seeing darkness in front of the eyes. (For example, when a person with deficiency constitution squats for a long time and stands up suddenly, they often experience darkness in their vision.)

Yun (vertigo/spinning sensation) is synonymous with "Yun" (movement/rotation), meaning rotation. The objects seen appear to be spinning rapidly like flying things, which is commonly referred to as "tou xuan" (spinning head). This is caused by the upward rushing of Wind-Fire. The Classics state that tremors and vertigo belong to Wind-Wood (Liver). Wind is the fluctuating manifestation of Fire Qi; Wind arises from Fire, and Fire is fanned by Wind. Observing flames rotating when wind blows makes this clear. (External Wind, Internal Wind, Hot Wind, and Cold Wind can all fan the Fire.) The Classics say that the essence and qi of the five zang and six fu organs all ascend and pour into the eyes. Therefore, the ability of the eyes to see is due to the spiritual clarity provided by the essence and qi of the organs. These ascending essence and qi must remain quiet and unshaken so that objects appear stable. If stirred and rotated by Wind-Fire, then the objects seen will also rotate. This is a disease of the eye's essence and qi, not a rotation of the eyeball itself. However, the Classics also state that the eye system connects to the brain, emerging from the middle of the neck. When pathogenic factors (referring to Wind Pathogen) strike the neck deeply and enter the brain via the eye system, it causes "brain rotation" (a sensation of head spinning). Brain rotation pulls on the eye system, causing tension in the eye system, which leads to eye movement and dizziness. Zhao Yi-de stated that following stillness and tranquility is the transformation of Water, while agitation and disturbance are the functions of Fire. The head is dominated by the brain, which is the sea of marrow. The pupils of the eyes are also the essence of the Kidney. Both belong to Kidney Water, which prefers tranquility and dislikes agitation. Tranquility maintains inner clarity; agitation leads to scattering and confusion. Hence the mention of dizziness and brain rotation. Thus, Wind-Fire stirring indeed causes brain rotation and eye system tension, leading to visual dizziness. The Six Excesses (Wind, Cold, Summerheat, Dampness, Dryness, Fire), Seven Emotions (Joy, Anger, Worry, Thought, Sorrow, Fear, Fright), diet, phlegm, and fluid retention, among other pathogens, can all stir Fire and generate Wind. When Wind-Fire reaches extreme abundance, this occurs. Even robust individuals may experience it; it is not necessary to have a deficient constitution, though deficient individuals are more prone to it. Ignorant people invariably attribute it to deficiency. Observe drunk people with blurred vision; what does this have to do with deficiency? Liu Zongnong considered it an Upper Excess condition, while the Classics considered it an Upper Deficiency condition. This is not contradictory. Generally, "Deficiency" refers to Blood and Qi, while "Excess" refers to Wind-Fire and Phlegm-Saliva. Righteousness (Zheng Qi) is originally deficient, while Evil (Pathogens) becomes excessive. Phlegm-Saliva surges upward with Wind-Fire, where turbid Yin interferes with clear Yang. Therefore, those suffering from Head Wind and vertigo often have Phlegm-Saliva. Zhu Danxi said, "No Phlegm, No Vertigo"; recovery only occurs after the Phlegm is expelled.