Although the diurnal variation of blood glucose in normal people is influenced by a variety of factors, it can be regulated by nerves, endocrine and liver to stabilize blood glucose in the range of 3.9 to 7.8. Both under-eating and/or over-utilization can lead to low blood sugar. In adults without type 2 diabetes, blood glucose below 2.8 mmol/L is called hypoglycemia and may cause various uncomfortable symptoms, while for diabetic patients, hypoglycemia is diagnosed when blood glucose is below 3.9 mmol/L. Diabetic patients often have elevated blood sugar, so why do they have hypoglycemia again? Improper eating, exercise and medication can lower blood sugar excessively. Severe hypoglycemia can be life-threatening, so people with diabetes should not only prevent excessive blood glucose, but also not ignore hypoglycemia. Hypoglycemia can happen at any time, and once it happens, if it is not dealt with in time, its consequences will be unimaginable. In clinical work, we often encounter patients who are in coma due to hypoglycemia, and even some patients cannot wake up after a long hypoglycemic event, and eventually can only live in the state of “vegetative”. Therefore, diabetic patients should carry candy, cookies and other foods to prevent hypoglycemic episodes and patient help cards to facilitate timely rescue.