**Core Concept**
Sudden severe headache with altered sensorium in a nondiabetic, nonhypertensive adult male suggests a hemorrhagic stroke, which is a medical emergency requiring prompt diagnosis and treatment. The likely diagnosis is a subarachnoid hemorrhage (SAH), which is often caused by the rupture of an aneurysm or arteriovenous malformation (AVM) in the brain.

**Why the Correct Answer is Right**
The sudden onset of severe headache, often described as "the worst headache of my life," is a classic symptom of SAH. This is due to the rapid increase in intracranial pressure and the stretching of pain-sensitive structures in the brain. The altered sensorium is likely due to transtentorial herniation, which occurs when the increasing intracranial pressure pushes the brain structures across the tentorial notch, compromising the brainstem and leading to impaired consciousness.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while migraine can cause severe headache, it typically does not present with altered sensorium or rapid onset. Migraines often have a gradual onset and may be accompanied by other symptoms such as aura, nausea, and sensitivity to light.

**Option B:** This option is incorrect because while meningitis can cause headache and altered sensorium, it typically presents with fever, neck stiffness, and other systemic symptoms such as vomiting and altered mental status. Meningitis is an infection of the meninges, the protective membranes surrounding the brain and spinal cord.

**Option C:** This option is incorrect because while seizures can cause altered sensorium, they typically present with convulsions or abnormal movements rather than a sudden severe headache. Seizures can be caused by a variety of factors, including epilepsy, head trauma, or metabolic disorders.

**Clinical Pearl / High-Yield Fact**
The "worst headache of my life" is a classic symptom of subarachnoid hemorrhage, and prompt recognition and treatment are essential to prevent long-term neurological damage or death. Always consider SAH in the differential diagnosis of sudden severe headache, especially in patients with altered sensorium.

**Correct Answer:** C. Subarachnoid hemorrhage