The baby is likely to be significantly unwell from the time they were severely shaken. There may be vomiting, irritability, fits (seizures), drowsiness, and even coma. There is a range of severity in this condition, and some babies may be only mildly unwell. However, it will be clear to a parent / caregiver that their baby is not their usual self from the time that the shaking happened. They may be very fussy and go off their feeds, or vomit.