Regressing

I can feel my mind shutting down. I've been awake this long before, but I've never actually tried to do things that require a lot of thought after having been awake this long. My stunted syntax and reduced vocabulary reminds me of a Stephen King short story whose title I do not know.

It begins with some urgency in the first person. The narrator says something along the lines of "I need to get this down before it happens to me, so that those that come after us can know what happened."

The narrator then describes his younger brother. He'd always been different, been considered a genius, tried to change the world, etc. One day, while researching a dramatically lower murder rate in and around Waco, Texas, he discovers that there is something in the water that makes the local populace unusually passive. He calls this agent "The Calmative" and makes it his mission to distribute it around the entire world.

He eventually gets his wish; a massive volcanic eruption is predicted, so he seeds the volcano with the Calmative. When it blows, it spreads a cloud around the world, taking the Calmative with it.

That's where it becomes a Stephen King story.

Turns out, in addition to making people passive, the Calmative causes the extremely rapid onset of symptoms not unlike Alzheimer's. The entire time, the narrator makes more and more typing errors, and by the end of the story, he sounds like a first grader. End of the world.

Comforting, eh?

Update: I did some research, and it turns out that this was a short story called "The End of the Whole Mess," and it was published only in the October 1986 of Omni. It's collected in Nightmares & Dreamscapes.