Cluster headaches are rare and cause severe pain that tends to recur in the same way each time. Cluster headaches occur in groups, or clusters, and each attack lasts about 1 to 3 hours on average.
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Cluster headaches -- called cluster because of their pattern of striking in groups or clusters -- hit at the same time of day for a period of weeks or months, then vanish as suddenly and as mysteriously as they appeared.
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