source : http://www.mayoclinic.com/health/febrile-seizure/DS00346/DSECTION=causes
By Mayo Clinic staff
Most febrile seizures occur because of a sudden spike in body temperature, and most occur during the first day of a fever. But a febrile seizure may also develop as the fever is declining.
Usually, the fevers that trigger febrile seizures are caused by an infection in your child’s body:
Most common. The most common cause is a typical childhood illness, such as a middle ear infection or roseola — a viral infection that causes swollen lymph nodes, usually in the neck, and a rash.
Less common. A less common but very serious cause of sudden fever with seizures is an infection of a child’s brain and spinal cord (central nervous system), such as meningitis or encephalitis.