A child’s sudden crying and not waking up may be due to nightmares, calcium deficiency and high fever. 1. Nightmare: When the child sleeps and has a nightmare, he or she will suddenly cry when frightened by the scene in the nightmare. However, it is difficult to wake up because the child is still sleeping and immersed in the nightmare. 2. Calcium deficiency: Children with calcium deficiency have increased excitability of the cerebral cortex and may suddenly cry out at night, often accompanied by sweating and twitching of the limbs, etc. If the child is in deep sleep at this time, it will be difficult to wake him up. If the child is in deep sleep at this time, he or she may not wake up. 3. High fever: A child with high fever after sleeping may suddenly cry out due to discomfort. However, because of its fuzzy consciousness, it is difficult to respond to the shouts of those around him, thus the phenomenon of not waking up. If the child suddenly cries and does not wake up, if accompanied by uncomfortable symptoms, we should go to the hospital as soon as possible, the doctor according to the specific conditions of the diagnosis and treatment plan, so as not to delay the condition.