Separation anxiety disorder or SAD refers to a mental health disorder that begins in childhood and is characterized by worrying that is out of proportion to the situation of temporarily leaving home or otherwise separating from loved ones;

a childhood disorder characterized by intense, excessive, enduring, and inappropriate fear and anxiety, in some children children and adolescents lasting at least weeks, concerning separation from home or caregivers. The child may develop excessive worrying to the point of being reluctant or refusing to go to school, being alone, or sleeping alone. The child may also experience repeated nightmares and complaints of physical symptoms such as headaches , stomach aches, nausea , or vomiting.