Thunderclap headache is a severe and acute headache that reaches maximum intensity in under one minute and lasts for more than five minutes. Thunderclap headaches may be associated with symptoms such as photophobia, nausea, vomiting, neck pain, focal neurological symptoms or loss of consciousness. Subarachnoid haemorrhage (SAH) accounts for 10-25% of all thunderclap headaches and, despite advances in medical technology, has a 90-day mortality of 30%. Up to a quarter of cases of SAH are misdiagnosed, often through failure to follow guidance.