眩，惑乱也，从目从玄。玄，黑暗也，谓眼见黑暗也。（虚人久蹲陡起，眼多黑暗是也。）
晕与运同，旋转也，所见之物皆旋转如飞，世谓之头旋是也。此风火上冲使然。经
以掉眩属风木，风即火气之飘忽者，风从火生，火藉风煽，观焰得风而旋转，可见
矣。（外风、内风、热风、冷风，皆能煽火。）经言五脏六腑之精气，皆上注于目，
然则目之能视
者，乃脏腑之精气灵明为之也。此上注之精气。必安静不摇，而后 物有定，若为
风火所煽而旋转，则所见之物亦旋转矣。此乃目之精气为病，非目睛之转动也。然
经谓目系属于脑，出项中，邪（邪指风邪言）中项入深，随目系入脑则脑转，脑转则引目
系急，目系急则目转眩。赵以德谓顺静宁谧者水之化，动扰挠乱者火之用。头以脑
为主，脑者髓之海，目之瞳子亦肾之精，二者皆属肾水，喜宁静而恶动扰。宁静则
清明内持，动扰则散乱昏惑，故目眩脑转云云。则风火煽动，固有脑转系急，而目
转眩者乎。六淫七情，饮食痰水诸邪，皆能动火生风，风火盛极即然，虽壮实人亦
有之，不必虚弱也，但虚者多耳。昧者定归之虚，试观醉人眼花，与虚何涉哉。刘
宗浓以为上实，经以为上虚，非相悖也。盖虚者血与气也，实者风火与痰涎也，正
自虚而邪自实也。痰涎随风火上壅，浊阴干于清阳也，故头风眩晕者多痰涎。丹溪
谓无痰不作眩，必搐去而后愈。
眩，就是惑乱的意思，由“目”和“玄”组成。“玄”，意为黑暗，指眼前感到黑暗。（例如体虚之人久蹲后突然站起，眼前常出现黑暗的情况，便是如此。）
晕与“运”字相通，意为旋转，感觉所见之物都在飞速旋转，世人称之为“头旋”。这是风火之气上冲所致。《内经》认为掉眩（肢体动摇、头晕目眩）归属于风木（肝），风即是火气飘忽不定的表现，风从火中生发，火借风势煽动，观看火焰遇风而旋转，道理便显而易见了。（外风、内风、热风、冷风，都能煽动火势。）《内经》说五脏六腑的精气，都向上灌注于目，那么眼睛之所以能视物，是靠脏腑精气的灵明作用。这些上注的精气，必须保持安静而不摇动，然后物体才能显得稳定；如果被风火煽动而旋转，那么所见之物也就随之旋转了。这是眼的精气发生病变，而不是眼球本身的转动。然而《内经》又说目系连接于脑，出于项部中间，邪气（此处指风邪）中于项部深入，随目系进入脑部则导致脑转（头部昏沉旋转感），脑转则牵引目系紧张，目系紧张则导致眼球转动、眩晕。赵以德认为顺应静宁谧的是水的化生特性，动荡扰乱的是火的作用。头部以脑为主宰，脑是髓之海，眼睛的瞳仁也是肾之精气，二者都属于肾水，喜欢宁静而厌恶动荡扰乱。宁静则清明内敛持守，动荡扰乱则散乱昏惑，所以有目眩脑转的说法。那么风火煽动，确实会导致脑转、目系紧张，进而引起目转眩晕。六淫（风、寒、暑、湿、燥、火）、七情（喜、怒、忧、思、悲、恐、惊）、饮食、痰饮等诸种邪气，都能动火生风，风火盛极就会这样，即使是身体壮实的人也会有这种情况，不一定非要是虚弱体质，只是虚弱的人更多罢了。愚昧的人一定将其归结为虚证，试看醉酒之人眼花，这与虚证有什么关系呢？刘宗浓认为是上实，《内经》认为是上虚，这并不矛盾。大概虚是指血与气而言，实是指风火与痰涎而言，正气本虚而邪气自盛。痰涎随风火上壅，浊阴干扰清阳，所以患头风眩晕的多有痰涎。朱丹溪说无痰不作眩，必须祛除痰涎后才能痊愈。
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.