Declining stocks worry people sick, if hospital records are any guide.

A one-day drop in equities of around 1.5% is followed by an increase of about 0.26% in hospital admissions on average over the next two days, according to a March 2013 study by Joseph Engelberg and Christopher Parsons, associate professors of finance at the University of California at San Diego. The impact on psychological conditions such as anxiety or panic attacks is even stronger and more immediate, with admissions jumping twice that much in one day.

“It’s a very straightforward result,” Engelberg said at last month’s American Economic Association’s annual meeting in Philadelphia, where he presented the findings. The results were based on almost three decades of daily admission data for California hospitals. Hospitalizations rise on days when shares fall, and “people are hospitalized disproportionately for mental conditions.”

Equity-market losses appeared to induce 3,700 market-related hospitalizations a year in California, which implies visits add roughly $650 million a year to U.S. health-care costs when data from the most-populous state are extrapolated nationally, Engelberg and Parsons estimated. They cited Census Bureau data showing an average hospitalization event costs around $21,000.

Mental-health admissions show up more quickly, with virtually the entire effect appearing the first day, the paper shows. That was especially true on October 19, 1987, when admissions jumped more than 5% after the Standard & Poor’s 500 index plunged 20% in the “Black Monday” crash, the researchers wrote.

“People get stressed out and anxious and depressed when the stock market performs poorly,” Engelberg said in an interview after his presentation. The effect of a large market drop is twice as strong during periods of low volatility because “extreme returns are more surprising to investors,” Engelberg and Parsons concluded.

“Your expectations are set by what you experienced in the recent past,” Engelberg said. “If it wasn’t very bumpy and you see a big bump down today, that’s more likely to get you depressed or stressed or anxious than if you saw a lot of bumps in the past year.”