Epilepsy is a neurological disorder with an annual incidence in the Netherlands of 30 per 100,000 people. We present two cases of a patient admitted to the emergency department upon experiencing a generalized seizure. In each case, severe metabolic lactic acidosis was identified through routine laboratory diagnostics. Based on their clinical presentation, we had no reasons to suspect another cause of this severe acidosis apart from the seizure. We repeated arterial blood sample one to two hours later and found that both pH and lactate were normalized. Severe lactic acidosis may occur in patients who experience seizures but otherwise do not require treatment. Taking an arterial blood sample from these patients in the emergency setting will be of limited value, because in most patients hyperlactatemia in the postictal state is self-limiting. In some patients, however, a persistent hyperlactatemia may indicate a serious underlying pathology. It is therefore advisable to repeat an arterial blood sample a few hours later.