Sudden crying during sleep may be caused by physiological factors such as hunger, fright, or diseases such as intestinal spasm and rickets. 1. Physiological factors: if the child is hungry, sleep frightened, nervous, may lead to sleep suddenly cry. If there are no other symptoms, there is no need to worry, this is a normal phenomenon. 2. Intestinal spasms: Intestinal spasms are mainly caused by gastrointestinal gas, allergies, improper diet, and adverse psychological factors. The child may have paroxysmal acute abdominal pain, when abdominal pain can appear to sleep suddenly crying. 3. Rickets: Rickets is caused by various reasons leading to vitamin D deficiency in the body, which can cause abnormal calcium and phosphorus metabolism in the body. Affected children show irritability, excessive sweating, crying at night, sleep disturbance and so on. There are many reasons why children suddenly cry in their sleep, and it is recommended that parents bring their children to regular hospitals to undergo relevant examinations to identify the cause of the disease. Once the diagnosis is confirmed, you should actively cooperate with the doctor to take relevant treatment measures.