**Core Concept**
Intractable hiccups can be a symptom of various underlying conditions, including psychiatric disorders, neurological diseases, and even malignancies. However, the relationship between hiccups and a patient's perception of impending doom or death is particularly relevant in this scenario.

**Why the Correct Answer is Right**
The most probable diagnosis in this case is **Situational Anxiety or Conversion Disorder**, characterized by a physical symptom (in this case, hiccups) that is not explained by a medical condition, but rather by a psychological or emotional distress. This condition is often associated with a strong emotional or psychological trigger, which in this scenario might be the patient's fear of gastric cancer. The patient's radiological investigations proving the contrary do not rule out the possibility of a psychiatric component to his symptoms.

**Why Each Wrong Option is Incorrect**
**Option A:** Gastric cancer is a possible cause of hiccups, but the patient's radiological investigations have already ruled this out.
**Option B:** While certain neurological conditions can cause hiccups, there is no indication in the scenario that this patient has a neurological disorder.
**Option C:** Intractable hiccups can be a symptom of various conditions, but this patient's symptoms are more likely related to a psychiatric or emotional cause rather than a physical one.

**Clinical Pearl / High-Yield Fact**
In patients presenting with unexplained physical symptoms, it is essential to consider a psychiatric or emotional component, as these can be just as debilitating and require appropriate treatment.

**Correct Answer: C. Conversion Disorder.**