Sarah Fader, a social media consultant in Brooklyn who has generalized anxiety disorder, texted a friend in Oregon about an impending visit, and when a quick response failed to materialize, she posted on Twitter to her 16,000-plus followers. "I don't hear from my friend for a day—my thought, they don't want to be my friend anymore," she wrote, appending the hashtag #ThisIsWhatAnxietyFeelsLike.

Thousands of people were soon offering up their own examples under the hashtag; some were retweeted more than 1,000 times. You might say Ms. Fader struck a nerve. "If you're a human being and you're not anxious," she said on the telephone, "there's something wrong with you."

Editor's Note: This same article also argues, "As depression was to the 1990s … so it seems we have entered a new Age of Anxiety … Today’s Americans can make a pretty strong case that they are gold medalists in the Anxiety Olympics."