Traumatic shock would do well to explain it.

http://www.trauma-pages.com/s/t-facts.php

emotional swings -- like crying and then laughing.

Sorry, but I doubt that the government would manufacture a tragedy like this, especially one so large-spread to take a stronger stance on gun-control, simply because what they're proposing and stuff isn't fixing the source of the problem, it just appears to to the public.