Frightened parents bring in their young child who has just had a first-ever generalized seizure with jerking tonic-clonic movements and loss of consciousness (LOC), followed by a period of postictal obtundation that gradually resolves within 30 minutes. The patient has completely recovered by the time the child is brought to your attention. The parents describe their child becoming cyanotic with breathing difficulty, unresponsiveness, and jerking eye movements during the seizure. The child may be found to have a fever, and there may be a family history of febrile seizures. A vaccination with diphtheria and tetanus toxoids and whole-cell pertussis vaccine may have been administered earlier in the day or 1 to 2 weeks following a measles, mumps, and rubella vaccination.