Which of the following is a key feature of cluster headaches?

Cluster headaches are characterized by a series of painful attacks that occur in clusters or cycles. A key feature of these headaches is that they often present with significant autonomic symptoms, which include tearing (lacrimation) and nasal congestion on the same side as the pain. This feature is notable because it distinguishes cluster headaches from other types of headaches.

The attacks are typically unilateral and severe, often described as a "burning" or "piercing" pain, and they can occur multiple times a day during a cluster period. Patients might also experience accompanying symptoms such as redness in the eye and swelling of the eyelid on the affected side.

While cluster headaches can occur at any time, they frequently happen around the same time each day, which aligns with the description of periodicity rather than simply being a common occurrence in the morning. This period of activity may also coincide with a particular season, but the significant tearing remains a hallmark symptom.

Other characteristics that are less prominent but pertinent include the fact that individuals might find relief from the pain through actions like pacing or moving, unlike many other headache types where rest is preferred. This further emphasizes the unique nature of cluster headaches, supported by their distinctive physical symptoms during acute attacks.