I suspect it is a systemic human reaction to shock, and/or enhanced stress. Sometimes our visual perceptions cannot absorb what we are seeing so our subconscious mind breaks the elements down into fractional pieces so that we can understand it better and realise what we have experienced.
It is opposite, but similar to the sensation of time flying by � for instance if you are a nervous orator and you do a speech in front of a lot of people, often you might find that you felt the time of the speech flew by or if you are really struggling, that it dragged. For the listeners who are not shocked or stressed, it usually drags!