Does anyone remember a horror book, probably from 1990s or earlier, set in a small town where there was a release of some experimental gas of some sort that caused everyone to go crazy in different and bizarre ways? There was a gross scene of a guy involving severe stomach cramps and a horde of little red spiders crawling out his toilet.

I thought it a King book, but now I'm thinking not. I don't want to read it so much as figure out what it was... ;-)

TIA!