Patient presents with sudden onset of severe headache, described as "the worst headache of my life," consistent with a suspected subarachnoid hemorrhage (SAH).  Onset was sudden while [activity at onset, e.g., exercising, at rest].  Associated symptoms include nausea, vomiting, neck stiffness, photophobia, and decreased level of consciousness.  Neurological examination reveals [specific neurological findings, e.g., nuchal rigidity, positive Kernig's and Brudzinski's signs, cranial nerve deficits].  Patient's medical history includes [relevant medical history, e.g., hypertension, smoking, family history of aneurysms].  Differential diagnosis includes migraine, meningitis, intracranial hemorrhage, and cerebral aneurysm.  Initial computed tomography (CT) scan of the head without contrast was performed to evaluate for subarachnoid blood.  If CT is negative and clinical suspicion remains high, lumbar puncture (LP) will be considered to analyze cerebrospinal fluid (CSF) for xanthochromia and red blood cells.  Cerebral angiography is planned to identify the source of bleeding, such as a ruptured aneurysm or arteriovenous malformation (AVM).  Treatment plan includes supportive care, pain management, blood pressure control, and neurosurgical consultation for possible aneurysm clipping or coiling.  Patient's condition is being closely monitored for complications such as vasospasm, hydrocephalus, and seizures.  ICD-10 code I60.9 (Subarachnoid hemorrhage, unspecified) is assigned.  Continued monitoring and reassessment are warranted.