my baby suddenly vibrate wht is the reason

A. Hai good morning !! Sudden shaking/ jerking during sleep is common for 5-10 seconds. If you observe more shaking like fits for more than 30 seconds to a minute ,any raise in temperature(high fever) then take medical assistance. During high fevers few babies will get seizures(fits) for 2-3 minutes which is not normal so make sure that temperature wont raise 100 degress do sponging to control high fever if any.