Babies fall asleep with a startle may be caused by noisy sleep environment, vitamin D deficiency rickets, brain damage and other reasons. 1. Noisy sleep environment: the baby’s central nervous system development is immature, the environment is noisy, light stimulation and other factors lead to the baby fell asleep with a startle, as the baby grows older, the cerebral cortex development will gradually improve. 2. Vitamin D deficiency rickets: baby calcium deficiency or vitamin D deficiency can easily lead to nerve excitation, slight stimulation will appear to fall asleep with a startle, give the baby appropriate vitamin D or calcium supplements will gradually improve. 3. Brain damage: hypoxic ischemic encephalopathy, premature infant brain white matter lesions and other brain damage syndrome can also lead to the baby fall asleep with a startled situation, need to improve the timely medical examination comprehensive judgment. If the baby falls asleep with a frightening situation by improving the sleep environment can not be relieved in time, should consult the doctor in time, under the guidance of the doctor to clarify the diagnosis, targeted treatment.