2.
A wall of solid sound turned the world white. Sherlock had never experienced anything quite like it as for a perfectly lucid moment the world turned itself inside out so that sight and sound and up and down was meaningless.
Then the world came back sharp and painful but still upside down with no air to breathe and his eyes burned without his brain sorting what he saw and his ears were ringing and useless and for some reason the entire world tasted like chlorine. By the time his thoughts aligned into any sort of order and he realized that he was underwater it was already too late.
He flailed his limbs; he had seen people swimming before and understood the basic concept but somehow instead of his head bursting free to the surface, he found only concrete and the water was heavy and squeezed and burned and there were no green things growing to entangle him, where was Rupert, no John…and he had to breathe, and large hands were on his head holding him down…no, Mycroft had saved him, he was…there was no…
He took a breath. The water burned. The world faded.