**Core Concept**
Increased cough at night in a child is suggestive of gastroesophageal reflux disease (GERD). GERD is characterized by the reflux of stomach contents into the esophagus, causing irritation and subsequent coughing. This is often precipitated by lying down, which increases intra-abdominal pressure and facilitates gastric reflux.

**Why the Correct Answer is Right**
The mechanism behind GERD-induced cough involves the vagal stimulation of the esophagus by the acidic gastric refluxate. This stimulation activates the cough reflex, leading to increased coughing at night. The acidic nature of the refluxate activates the vagal afferent fibers, which are sensitive to acid and are located in the esophageal mucosa.

**Why Each Wrong Option is Incorrect**
**Option A:** Asthma is less likely as it typically presents with wheezing and shortness of breath rather than isolated cough. While asthma can cause coughing, the pattern of increased cough at night is more characteristic of GERD.
**Option B:** Cystic fibrosis is a genetic disorder that affects the respiratory and digestive systems, but it typically presents with chronic respiratory symptoms such as recurrent pneumonia and bronchiectasis, rather than isolated cough.
**Option C:** Foreign body aspiration can cause coughing, but it is typically a sudden event rather than a gradual increase in coughing at night.

**Clinical Pearl / High-Yield Fact**
A key clinical correlation is that the symptoms of GERD, including cough, may be exacerbated by lying down, bending, or heavy meals, and may be relieved by elevation of the head of the bed or antacids.

**Correct Answer: C**