**Core Concept**
A lumbar puncture (LP) in a patient with raised intracranial tension (ICT) can lead to a sudden decrease in intracranial pressure (ICP), causing a compensatory increase in cerebral blood flow (CBF) and potentially resulting in cerebral herniation. This is known as the "Cushing's reflex" or "Cushing's response," which is a physiological mechanism that helps to regulate ICP.

**Why the Correct Answer is Right**
The correct answer is related to the sudden decrease in ICP causing a compensatory increase in CBF, which can lead to cerebral edema and herniation. This is due to the increased pressure exerted by the cerebrospinal fluid (CSF) on the brainstem and cerebellum. The rapid decrease in ICP can also lead to a transient increase in systemic blood pressure, which can cause a further increase in CBF, exacerbating the situation.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not directly related to the scenario described. While seizures can be a complication of LP, they are not the most likely cause of death in this situation.
* **Option B:** Hypotension is not typically associated with the Cushing's reflex, which is characterized by increased blood pressure. Therefore, this option is unlikely to be the correct answer.
* **Option D:** While cardiac arrest can be a complication of LP, it is not the most likely cause of death in this scenario, given the context of raised ICT and the Cushing's reflex.

**Clinical Pearl / High-Yield Fact**
The Cushing's reflex is a critical concept to remember when performing a lumbar puncture in patients with raised ICT, as it can lead to a sudden and potentially fatal outcome if not recognized and managed promptly.

**Correct Answer: C. Cerebral herniation**