I used to get this a lot - I'd be dozing peacefully, then would hear a loud bang with a hypnic jerk and auditory startle response (a white flash). I just put t

I used to get this a lot - I'd be dozing peacefully, then would hear a loud bang with a hypnic jerk and auditory startle response (a white flash). I just put the whole thing down to nervous system noise, like closed-eye hallucination and tinnitus, though it went away when I got a bit older and stopped drinking caffeine after 3PM.