A woman in her thirties, who had never had symptoms of dry mouth, excessive drinking, excessive urination and wasting, suddenly developed dizziness, blurred eyes, cold sweat all over her body and shaking hands in the morning at work, and only got better after eating a little. She thought she was too tired, but she had experienced this twice before. When she went to the hospital for oral glucose tolerance test, her fasting blood sugar was 4.6mmol/L, 1 hour postprandial blood sugar was 17.9mmol/L, 2 hours postprandial blood sugar was 11.5mmol/L, 3 hours postprandial blood sugar was 6.3mmol/L and 4 hours postprandial blood sugar was 2.6mmol/L. When her blood was drawn at 4 hours, the symptoms of dizziness, blurred eyes and cold sweat appeared again, which were definitely caused by hypoglycemia. It was definitely caused by hypoglycemia. Based on this result, we can diagnose her with diabetes mellitus. Don’t we usually see high blood sugar in diabetes? Why does this person have frequent hypoglycemia? Her insulin levels were 10.6 mU/L fasting, 83.9 mU/L 1 hour after meal, 111.5 mU/L 2 hours after meal, 69.2 mU/L 3 hours after meal, and 22.6 mU/L 4 hours after meal, and we found that her insulin levels were significantly elevated at all times, which we call insulin resistance. In normal people, insulin levels rise to the highest level half an hour after drinking glucose, but she did not reach the highest level until two hours, and it did not fall to the basal level until four hours, which is a typical delay in insulin secretion. This is a typical case of delayed insulin secretion, which means that the blood glucose rises when the insulin should be high but does not rise, and low blood glucose occurs when the insulin should be low but does not fall. From this case, we should get to know diabetes again. Diabetes is not simply an increase in blood sugar, but a decrease in our body’s ability to regulate blood sugar within a stable range, resulting in blood sugar not being able to stay within the normal range, which will cause harm to the body whether the blood sugar rises or falls.