Cluster headache is a common type of headache occurring in groups or 'clusters,' with severe pain often on one side of the head and related symptoms like nasal congestion and eye redness. While the exact cause is unclear, abnormalities in the hypothalamus are believed to play a role, and alcohol can trigger attacks. The condition is rare, affecting fewer than 1 in 1,000 adults, and advancements in diagnosis and treatment options are expected to influence the market positively in the coming years.