A persistent confusional state after convulsive status epilepticus should raise suspicion for what diagnosis?

Non-convulsive status epilepticus.

If EEG monitoring is not immediately available - as is the case in many EDs, then empiric treatment with benzos looking for a paradoxical improvement in mental status should be considered.

Source

Goldstein, J. MD. "Status Epilepticus in the Pediatric Emergency Department." Clin Ped Emerg Med. 2008. v 9: 96-100.