The common causes of babies suddenly crying at night sleep are: physiological reflexes, rickets, digestive discomfort and so on. 1. Physiological reflexes: younger babies can not speak, usually by crying to express their demands. If the baby sleeps at night with hunger, bedwetting, too tight clothes lead to discomfort, it will remind parents by crying. 2. Rickets: This is usually caused by a lack of vitamin D and calcium, which in turn can manifest as sudden crying at night. In addition, excessive sweating, occipital baldness, and flared rib margins may also occur. 3. Digestive disorders: If the baby eats too much before going to bed at night, resulting in indigestion, or if the abdomen is cold at night, resulting in gastrointestinal spasms and colic, it can cause the child to cry suddenly at night. If your child cries more than once, you need to be vigilant and go to the hospital in time to determine whether there is an acute abdominal condition such as intussusception or intestinal obstruction. It can be seen that there are physiological and pathological reasons for babies to cry suddenly at night, and if accompanied by other discomforts, it is recommended to seek medical treatment as soon as possible.