I'm pretty sure it's hard to get a grand mal seizure from a concussion, but I know focal seizures can occur.
Common causes of seizures:
-Stroke or transient ischemic attack (TIA)
-Severe concussion
-Alzheimer's disease
-Traumatic brain injury
-Infections, including brain abscess, meningitis, encephalitis, and AIDS
-Brain problems that are present at birth (congenital brain defect)
-Brain injury that occurs during or near birth
-Metabolism disorders that a child may be born with (such as phenylketonuria)
-Brain tumor
-Abnormal blood vessels in the brain
-Other illness that damage or destroy brain tissue
So unless any of those things on that list have happened to or apply to you, I see no reason why you should worry.