The only pattern I can think of is that it tends to happen more often when I am more in need of sleep or more tired I guess. Yeah, lately it makes me feel like the doorbell was ringing. Such a weird thing. Us clusterheads def. have some quirky issues so it's good to try and find correlations. My spectrum of nero type issues is CH, EHS, panic attacks, cold seizures, ringing in the ears, mild tremors in the hands.....