A 4-month-old baby’s sudden crying in the middle of the night may be caused by physiological factors such as improper diet and environmental factors, as well as vitamin D deficiency, night terrors, and other factors such as indigestion. 1. Physiological factors: 4-month-old babies who eat too much before going to bed or feel hungry while sleeping may show sudden crying. In addition, the baby sleeping environment is too noisy, as well as the sleeping environment is too cold or too hot will make the baby suddenly cry in the middle of the night, these are normal physiological performance. 2. Vitamin D deficiency: Vitamin D deficiency may be caused by insufficient sunlight, chronic diarrhea, and too little vitamin D in breast milk. Patients will have night waking, crying, irritability, excessive sweating, bone deformities and other manifestations. If vitamin D deficiency occurs at 4 months of age, there will be symptoms of sudden crying in the middle of the night. 3. Nocturnal Alarm Syndrome: The cause of Nocturnal Alarm Syndrome is not yet clear, and it is considered to be related to heredity and being frightened. Patients will suddenly cry and scream during sleep, accompanied by a strong sense of fear, shortness of breath, rapid heart rate, sweating, pupil dilation and other manifestations. Therefore, 4-month-old lesions with nocturnal terrors will be manifested as sudden crying in the middle of the night. 4. other: 4 months baby suddenly crying in the middle of the night may also be indigestion, infantile eczema, otitis media, colic and other causes. 4 months lesions suddenly cry in the middle of the night, there may be other reasons, it is recommended to go to the hospital, improve the examination to clarify the cause, under the guidance of the doctor to give targeted treatment or treatment.