**Core Concept**
Tetralogy of Fallot is a congenital heart defect characterized by four components: ventricular septal defect, pulmonary stenosis, right ventricular hypertrophy, and an overriding aorta. Patients with this condition are at increased risk of developing cyanotic spells, which can be triggered by factors such as infection, fever, or dehydration.

**Why the Correct Answer is Right**
The symptoms described in the scenario, including severe headache, nystagmus, and ataxia, are suggestive of a posterior fossa mass lesion or increased intracranial pressure. Given the patient's recent initiation of a "pink, bubble-gum tasting antibiotic," the likely culprit is aminoglycoside-induced ototoxicity, which can cause vestibular dysfunction and nystagmus. However, the more concerning possibility is that the antibiotic has raised the patient's intracranial pressure, possibly due to its ototoxic effects or the underlying infection itself. The most appropriate first test to order in this scenario would be a **non-contrast head CT scan** to rule out any intracranial hemorrhage, mass lesion, or other causes of increased intracranial pressure.

**Why Each Wrong Option is Incorrect**
**Option A:** A lumbar puncture would not be appropriate in this scenario due to the risk of brain herniation in the presence of increased intracranial pressure.

**Option B:** An MRI of the brain would be a more detailed imaging study, but it is not the most appropriate first-line test in this emergency situation.

**Option C:** An electroencephalogram (EEG) may be useful in evaluating seizure activity but would not be the first step in evaluating this patient's acute symptoms.

**Clinical Pearl / High-Yield Fact**
Aminoglycoside ototoxicity can cause vestibular dysfunction, which may manifest as nystagmus, vertigo, or ataxia. This is an important consideration when using these antibiotics in patients with underlying neurological conditions or those at risk of increased intracranial pressure.

**Correct Answer:** C. Non-contrast head CT scan