Four-month-old babies suddenly cry in the middle of the night may be related to hunger, shock, lack of vitamin D and so on. 1. Hunger: If the baby did not take milk before going to bed, or if the milk is relatively small, the baby may cry when he is hungry. 2. Scaring: If the baby is frightened while sleeping, such as thunder or unusual noise, it may also cause the baby to cry suddenly in the middle of the night. 3. lack of vitamin D: baby vitamin D deficiency, more easily irritable, frightened, resulting in sudden crying phenomenon. Four-month-old baby suddenly cried in the middle of the night, there may be other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor’s treatment.