(HealthDay News) -- Cluster headaches are bouts of severe, recurring pain on one side of the head. They may strike in clusters, occurring daily or several times a day for weeks at a time. The exact cause of cluster headaches isn't understood.
The University of Virginia Health System says risk factors for cluster headaches are thought to include:
Changes in barometric pressure.
Sleep schedule changes.
Taking certain medications, including nitroglycerin.