My synaesthesia symptoms are generally much less "violent" and far more useful most of the time.
When I am trying to sleep, though, I have to let go of my will and stop forcing myself beyond the confusion or finding differentials or factors and just allow the entire spectrum of sights and sounds to unfold and dance the way they want. I could never get to sleep, if I was still doing an Atlas impression in the face of my crossovers. I have to just set the world down and release my mind to sleep.
(Someone here, I think it was Renaeden, once asked me how a person could possibly awaken over-stimmed, but I almost always awaken near panic and have to find the outside world by force of will.)
I doubt that I would notice anything special about another flash of color or light from the surrounding sounds.