Subarachnoid hemorrhage is a medical condition where there is bleeding in the space between the brain and the tissues covering it, known as the subarachnoid space. This bleeding can occur due to a ruptured aneurysm or head injury, leading to sudden and severe headaches, often described as a "thunderclap" headache. Other symptoms may include nausea, vomiting, and sensitivity to light. This condition is serious and requires immediate medical attention. Doctors may perform a CT scan or lumbar puncture to diagnose the hemorrhage. Treatment often involves managing the bleeding and preventing complications, which may include surgery or medication to control blood pressure and reduce the risk of further bleeding.