On the other hand . . . . this is from a 2010 study sponsored by ClusterBusters that collected data from more than 1100 people with CH. (Rozen and Fishman, "Cluster Headache in the United States of America.") The authors wrote, "The circadian periodicity of cluster headache is present but is not as common in the population as previously thought."
"Months of the year that cluster headache cycles would start.
In 41% of the survey responders, their cycles varied during the year, and there was no particular month the cycles would always begin. By percentages, the months of October (26%), September (21%), April (21%), March (20%), and November (20%) were the most likely for cluster headache sufferers to start a cycle. The remainder of the months of the year were evenly distributed with 11-13% stating their headaches cycles would start during these particular months. The lowest percentage was noted for the month of June at 10%."