**Core Concept**
Cluster headaches are a type of primary headache disorder characterized by severe, unilateral, and short-lived headaches that occur in clusters or cyclical patterns. They are often associated with autonomic symptoms such as lacrimation, conjunctival injection, and nasal congestion.

**Why the Correct Answer is Right**
Option C, "Bilateral," is incorrect because cluster headaches are typically unilateral, affecting one side of the head. The pain is usually centered around the eye and can be accompanied by symptoms such as ptosis, miosis, and rhinorrhea. Cluster headaches are more common in males, with a male-to-female ratio of approximately 2.5:1. They often occur at the same time every day, usually between 2 and 3 am, and can be accompanied by autonomic symptoms such as lacrimation and nasal congestion.

**Why Each Wrong Option is Incorrect**
**Option A:** While cluster headaches are more common in males, the statement is true, but not relevant to the question about the characteristics of cluster headaches.

**Option B:** Cluster headaches are typically periorbital in location, affecting the area around the eye, which is correct.

**Option D:** Cluster headaches often occur in the early hours of the morning, typically between 2 and 3 am, which is correct.

**Clinical Pearl / High-Yield Fact**
Cluster headaches are often referred to as "suicide headaches" due to their intense pain, which can be debilitating and lead to suicidal thoughts in some individuals.

**✓ Correct Answer: C. Bilateral. Cluster headaches are typically unilateral, not bilateral.**