Every adult, at one time or another, has experienced nausea. Nausea is a subjective human sensation, like pain, a symptom that others cannot see or feel. When people see something malignantly stimulating such as dirty blood or thick sputum, they will feel nauseous; when artificially stimulating the root of the tongue and the pharynx, they will also feel nauseous. In fact, nausea is most often seen in gastric disease, followed by lesions of the biliary system, pancreas, liver spoils, and peritoneum. When nausea occurs, there is a feeling of distension and discomfort in the upper abdomen, aversion to food, and often accompanied by vomiting and plant nerve disorders, such as sweating, headache, dizziness, pallor, increased heart rate, and decreased blood pressure. So, how does nausea arise? Studies have shown that the mechanisms of nausea and vomiting are basically the same, both are responses to stimulation of the vomiting center of the brain (see the mechanism of vomiting). The difference lies in the strength of the impulse received by the vomiting center, when the impulse is weak, only nausea occurs, and when the impulse is strong, vomiting is produced.