What happened

Shares of offshore engineered services provider Oceaneering International (OII -0.27%) fell almost 12% in early trading on Feb. 24 and remain down 8.9% at 12:35 p.m. EST, riding the same rough seas that are driving the rest of the market down hard and fast today: coronavirus-induced global fear.

Man looking at a line on a chart that's sharply down.

Image source: Getty Images.

So what

Crude oil futures are enduring one of the worst days in the past year; West Texas Intermediate crude, the key American benchmark, is down 5.1%, while Brent, the most important global oil benchmark, is down more than 5.4%. This sell-off has a wide swath of oil stocks down sharply today, particularly companies that are typically the first to lose business when oil prices fall, along with companies with weaker balance sheets and less ability to ride out weak oil prices or demand.

It's not just energy stocks being affected today. At this writing, the Dow Jones Industrial Average (^DJI -0.16%) was down more than 2% on weekend news that the spread of COVID-19, the strain of coronavirus, had intensified in recent days, including in countries such as Italy, Japan, and South Korea.

Now what

The spread of coronavirus into these other countries has markets worried, because as we have already seen in China, efforts to halt the spread to save lives can have substantial impacts on economic output. In its February oil market report, the International Energy Agency has already warned that it expects global oil demand to fall in the first quarter -- the first quarterly decline in a decade -- due to China's efforts to lock down the spread of coronavirus.

Fast-forward to this weekend's news that the number of cases has increased sharply in several other countries that play a big role in the global economy and consume substantial amounts of energy, and you have a major sell-off. Moreover, the sell-off looks to be intensifying as retail investors start joining the professionals; in the time it's taken to write this note, the Dow is now down more than 3.3%, and Oceaneering shares have fallen more than 10.4%.

What should investors do? To start, don't sell in a panic. As my colleague Dan Caplinger notes, panic-selling almost always proves a mistake. A good idea for most investors today is to step away from your online brokerage and give the markets -- and your emotions -- some time to settle before making any sell decisions.