Cycles and the body clock
Attacks come in runs and almost on schedule. The hypothalamus is behind it.
Most people have the episodic form: weeks or months of attacks (the “cluster”), then months or years of remission. Cycles often return in the same season.
Within a cycle attacks keep a schedule too: many people are woken 1–2 hours after falling asleep, at the same hour.
Why
The rhythm is set by the hypothalamus, the brain's body clock. Brain scans show this area activating during attacks.
If cycles are predictable, prevention can start before the first attack. That is the main point of keeping a diary.
Sources
- May A. et al., Lancet, 1998 (hypothalamic PET)