Episodic, usually a cycle in Fall, although I got an extra one last year in Spring. Typically 4-6 weeks. I started getting them when I was 27, not diagnosed until I was 36. I did buy the cluster mask from Clusterheadaches.com and found it to work well. I prefer the mouth piece to the mask. I'm currently running a "welding O2" setup as I haven't been successful in getting Medical O2 setup, even though I got my nero to write a prescription.