**Core Concept**
The patient's symptoms suggest a possible recurrence of the brain tumor, which may have led to increased intracranial pressure (ICP). This is a medical emergency requiring prompt investigation and management.

**Why the Correct Answer is Right**
The correct investigation in this scenario is a non-contrast computed tomography (CT) scan of the brain. This is because it is a rapid and sensitive test for detecting acute hemorrhage, edema, or tumor recurrence, which can cause increased ICP and lead to the patient's symptoms. A CT scan can also help identify any hydrocephalus or other complications that may be contributing to the patient's condition.

**Why Each Wrong Option is Incorrect**
**Option A:** Magnetic Resonance Imaging (MRI) of the brain is not the first-line investigation in this scenario, as it takes longer to perform and may not be as readily available as a CT scan. While MRI can provide more detailed information about the brain and its structures, it is not as sensitive as CT for detecting acute hemorrhage or edema.

**Option B:** Lumbar puncture (LP) is not indicated in this scenario, as it can further increase ICP and worsen the patient's condition. LP may also be contraindicated if there is a suspicion of a space-occupying lesion or a mass effect.

**Option C:** Angiography is not the initial investigation of choice in this scenario, as it is more invasive and typically reserved for cases where vascular abnormalities are suspected.

**Option D:** Electrophysiology studies are not relevant to this scenario, as they are used to diagnose and manage disorders of the nervous system, such as epilepsy or neuromuscular diseases.

**Clinical Pearl / High-Yield Fact**
In cases of suspected increased ICP, it is essential to remember the "ABCs" of management: Airway, Breathing, and Circulation. Ensure the patient's airway is secure, breathing is adequate, and circulation is maintained to prevent further deterioration.

**Correct Answer:** C. Angiography