What is yang flourishing and yin declining?

Under normal circumstances, the human body is in a state of yin and yang balance, which is the secret of yin and yang in traditional Chinese medicine. But when foreign evil invades, or is congenitally deficient, or cannot support itself, there will be an imbalance between yin and yang, which is what you said. Traditional Chinese medicine believes that yang generally runs outside and plays a role of fixation and protection, while yin is mostly hidden in viscera, which is the foundation of human body. When yin deficiency occurs in the human body, that is to say, subtle substances are consumed excessively, and the balance of yin and yang is restricted. It may also be that the external fire poisons the invasion of yang evil, leading to the exuberance of internal yang and the decline of yin, which is mostly manifested as redness and fever, and even fainting words.