I'm 'in' a cluster right now and hadn't googled CH for a while, landed here and your post struck me right away.
a theory I have had for some years now is that my attacks start when I relax after a period of stress
I work in IT management and in my job drink bucketfuls of stress daily (luckily I sh1t out spreadsheets so, swings and roundabouts)
My Clusters happen approx 2-3y intervals but seem to always coincide with coming off a job, pootling around for a couple of weeks and then BANG. There are some other factors, diet, alcohol, sinus problems that actually 'trigger' me but I seem to be vulnerable when relaxing - in fact I've had notable attacks when on holiday (nice)