Sudden sitting up at night may be related to night terrors and calcium deficiency. 1. Night terrors: this disease may be related to genetic factors, frightened, etc., and often accompanied by abnormal behavior, screaming, fear and other symptoms at night when sleeping, so there may be a child sleep at night suddenly sit up in the middle of the night. 2. Calcium deficiency: If a child is deficient in calcium, sudden cramps and sleep disorders may occur, so the child may suddenly sit up at night. In addition, the child sleep suddenly sit up at night can be seen in other reasons, if the symptoms have been persisting, we recommend timely medical attention to clarify the cause of the disease, under the guidance of the doctor to carry out appropriate treatment.