What's happening?

The Twilight Zone: 1x3

Wordplay

Salesman Bill Lowery wakes up one morning and discovers, to his horror, that people around him are slowly degenerating their talk into gibberish that he cannot understand. His ability to communicate is needed more than ever when his son becomes sick. Lowery manages to get his son the treatment he needs and discovers he must relearn everything from scratch.

The Twilight Zone: Season 1 Episode 3
Oct. 04, 1985