In some children aged between 6 months-6 years a sudden increase in body temperature can lead to seizures(also known as fits) which are called febrile convulsions. During a febrile convulsion part or all of your child's body may shake and twitch and his or her eyes may roll back in the head. Although simple febrile convulsions can be frightening they usually last less than 15 minutes and your child should make a full recovery within one hour.
Attribution: BUPA