Glucose can be present in blood but the brain can be still unable to consume it due to diabetes (insulin absence) or some form of a mitochondrial disease (inability to transfer glucose to ATP via oxidation).

In both cases this is a panic situation from brain's point of view which is compensated by a spontaneous "stop" (seizure as OP seems to call it) and by injecting adrenaline with a corresponding response from endocrinal system (more glucose + more insulin).