The possible reasons for the sudden decrease in urine are as follows: 1. Acute renal failure, a sudden decrease in the filtration function of the kidneys, resulting in the inability to filter out water, leading to a sudden decrease in urine volume, accompanied by edema in the lower limbs or face and other parts of the body. Because metabolic waste accumulates in the body and cannot be excreted through urine, symptoms of metabolic waste accumulation such as dizziness, nausea and vomiting, called azotemia, may occur. Further examination of kidney function is needed to clarify the presence of acute renal failure. 2. Obstructive factors exist in the urinary tract, such as prostatic hyperplasia or urinary stones in men, causing ureteral or urethral obstruction. At this time, the kidney function is normal and the urine produced cannot be discharged out of the body because of the obstruction, so it shows as a sudden decrease in urine. However, at this time, the patient may suffer from back pain or urine holding, pain in the small abdomen, etc., or there is a condition of persistent pain in the urethra and inability to urinate. It is necessary to go to the hospital for examination and, if necessary, to give indwelling catheterization to drain the urine out of the body as soon as possible.