Wait a tick, we've already got that.
They come in bunches, with the initial one in any group triggering copycats. Some linger long in our memory, like Columbine, but most do not.
They happen anywhere, anytime. These "sleepers" awaken on their own timetable, but more stress in life brings more--go figure.
Naturally, our society is completely incapacitated by these developments. Work stops. Culture grinds to a halt. Politics ends. We are reduced to living in small, self-sufficient communities that squabble over remaining resources.
On the brighter side, I should soon be hearing about which teams I get to see at Lambeau this year.
If I can brave the badlands between here and Green Bay, I might risk the venture.