**Core Concept**
Haloperidol is a typical antipsychotic medication that can cause extrapyramidal side effects (EPS) due to its blockade of dopamine D2 receptors in the nigrostriatal pathway. This blockade leads to an imbalance in the dopaminergic and cholinergic neurotransmission, resulting in EPS.

**Why the Correct Answer is Right**
Vasanthi's symptoms of persistent deviation of the neck to the right side, which appeared after she started taking Haloperidol, are indicative of a dystonic reaction, a type of EPS. Dystonia is characterized by involuntary muscle contractions leading to abnormal postures. In this case, the dystonia is likely caused by the blockade of dopamine D2 receptors by Haloperidol, which disrupts the normal balance of neurotransmitters in the nigrostriatal pathway.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the scenario, as there is no mention of Parkinson's disease or other conditions that may cause tremors or rigidity.

**Option B:** This option is incorrect because akathisia is a type of EPS characterized by subjective feelings of restlessness and an urge to move, rather than a fixed posture.

**Option C:** This option is incorrect because tardive dyskinesia is a type of EPS that causes repetitive, involuntary movements, often involving the face and limbs, and is typically associated with long-term use of antipsychotic medications.

**Option D:** This option is incorrect because neuroleptic malignant syndrome (NMS) is a rare but life-threatening condition caused by the blockade of dopamine D2 receptors, but it is characterized by fever, muscle rigidity, and altered mental status, rather than a fixed posture.

**Clinical Pearl / High-Yield Fact**
Be aware that extrapyramidal side effects are common with typical antipsychotics like Haloperidol, and dystonic reactions can be treated with anticholinergic medications like benztropine or trihexyphenidyl.

**Correct Answer:** C.