Snape jolted awake: a single, full-body thrash, like a man stabbed through the heart, or hit with a deadly curse.
He blinked staring eyes and the air hissed past clenched teeth as his muscles slowly unwound out of the shock that had locked his whole body into a bowed rictus.
"Fuck," he panted absently as he sat up, gaze distant as he hurled all his attention outwards, probing the castle's defenses with panicked intensity.