What are cluster headaches?
A person with cluster headaches suffers from episodes of severe pain that occur behind one eye. Episodes of pain are brief and occur in groups, or clusters, over one to three days. Cluster headaches are more common in males and tend to occur at night. The exact cause of cluster headaches is unknown.

What are the symptoms of cluster headaches?
The most common symptom of cluster headaches is severe, constant, pain behind one eye. Symptoms generally last for an hour or two and then resolve without treatment. Headaches occur in clusters, over several days in a row. Additional symptoms of cluster headaches include: a drooping eyelid, facial flushing, facial swelling, eye tearing, and a runny nose.

How does the doctor treat cluster headaches?
Treatment for cluster headaches includes medications for pain and avoidance of substances that can trigger cluster headaches.