Used to happen to me, somewhat frequently as a child, less and less with age (I probably haven't had it in the past ten years). As I was falling asleep I starte

Used to happen to me, somewhat frequently as a child, less and less with age (I probably haven't had it in the past ten years). As I was falling asleep I started to hear some soft rhythmic noise repeating over and over, slowly at the beginning, then faster and faster until it ended in a really loud "bang" after which for a second my head felt entirely empty. (However the bang didn't feel like a real noise, more like an explosion inside my head). After I while I learned to recognise the pattern of speeding rhythmic sound and sometimes I would be able to stop it before the bang- lifting my head from the pillow was enough to break the sequence.