SAD or seperation anxiety disorder!
i used to have this when i was 9. here's the google definition:
"Children are especially prone to separation anxiety during times of stress.
Separation anxiety differs from normal clinginess. Children with the disorder can't think about anything but the present fear of separation. They may have nightmares or regular physical complaints. They may be reluctant to go to school or other places.
Treatment includes talk therapy and possibly anti-anxiety medication."
