Not a Nightmare

Alec's parents and siblings keep telling him that his mother trying to sacrifice him was a nightmare and not real. Clary keeps telling him that it's a nightmare and not real. All Alec can do is hold the fact that it was real and happened. Will he take matters into his own hands and get rid of the root of his nightmares? Post COLS. Oneshot. Prequel to Not Forgotten or Left Behind.