It is not painful. It is like a quick surge through my head. Maybe a spasm or even a jerk.

I do not hear anything when it happens. My head does not actually move although it feels like it could.

It moves my center of vision when it happens. I am pretty sure my eyes are not moving as in nystagmus. I do not seem them jitter when I look in the mirror.

I notice them most any time during the day and there does not seem to be any pattern or certian time of day when it is worse.

Calling it a zap is a good way to put it because it is there and gone, but with no pain. Weird.