Babies always suddenly cry in their sleep, may be physiological reasons, such as the baby wearing clothes or cover the quilt is not appropriate to cause. It may also be pathologic causes, such as colic, hernia and so on. 1. Physiological reasons: if the baby wear clothes or cover the quilt is not suitable, such as clothing or quilt is too thick, clothing or quilt on the hard things, etc., will lead to the baby feel uncomfortable so that the baby sleep always suddenly cry. 2. Pathological causes: (1) colic: baby colic is one of the most common causes of baby crying. Colic is associated with abnormal gastrointestinal dynamics, intestinal flora imbalance, lactose intolerance and so on. Baby sleep always suddenly cry may be caused by colic. (2) Hernia: Hernia is a condition in which an organ or tissue in the body leaves its normal anatomical site and enters a neighboring site through a weak point, defect, or aperture that is formed either congenitally or later in life. If your baby has a hernia, he or she may feel pain and other uncomfortable symptoms, which in turn may trigger your baby to sleep and always cry suddenly. There may also be other reasons why your baby cries all of a sudden during sleep, so it is recommended that you go to the hospital in time for a complete examination to determine the cause of your baby’s condition, and then give targeted treatment or therapy under the guidance of your doctor.