Four-month-old babies sleeping with a startle may be normal or abnormal, need to be divided into situations. The baby is relatively small, the central nervous system development is not yet fully mature, the control of the muscles is relatively weak, the baby in the sleep if the stimulus, such as changes in temperature, changes in light, etc. may cause excitement, resulting in a startle. The baby lacks vitamin D or calcium, the cerebral cortex excitability will increase, there will be a sleep phenomenon, may also be accompanied by sweating, occipital baldness and other phenomena. It is recommended to take your baby to the hospital for a checkup, if there is any abnormality, you need to be treated under the guidance of the doctor, follow the doctor’s instructions.