Seizures at the onset of SAH occur in 20% of patients . They are most likely to occur within the first 24 hours following injury, especially if a haematoma has caused cortical damage , but late seizures can develop up to 6 weeks after injury (occurring in 7-14% of patients with SAH. The greatest risk factors for seizure development are thought to be the amount of intracranial blood present and a rebleeding event . Anticonvulsants are not normally prescribed for the first seizure , and use of prophylactic anticonvulsants is associated with more risks than benefits . Subclinical seizure activity can occur reported a 38% incidence of subclinical seizure activity in 48 comatose patients following SAH. Physiological changes (elevated heart rate, blood pressure and respiratory rate) were noted in these patients at the time of the seizure activity. If there is evidence of subclinical seizure activity, treatment of the activity should be considered. Mrs S showed no signs of seizure activity during the acute phase of her haemorrhage.