When I go to bed at night and everything is silent and I begin to get asleep, but with my consciousness still a little bit awake, if an abrupt sound is made, like the one produced by a hard object striking against the floor, I can see in my mind an abrupt regular image full of bright lines. That lines are commonly alternating white and black, but i can see coloured lines too. The flash lasts a very very short time, first the abrupt sound and inmediatly after that the flaching lines. I searched the internet and couldnt find nothing similar. Did anyone have this experience before? Does someone knows the cause. These lines dont worry me, but I feel very curious about them.