It's hard to sit tight during uncertain times. But when it comes to long-term investing, it's the best time to do just that.

U.S. stock markets have plunged due to a combination of falling oil prices and worsening coronavirus fears. The rout on Monday knocked 7.6% off the S&P 500 index, which is now down 18.9% from its record peak reached just last month.

And the wild ride is likely to continue as the world tries to contain COVID-19 and grapple with its fallout. The virus has infected more than 110,000 worldwide and is present on every continent except Antarctica. Containment is proving difficult and concerns are growing that it will cripple the global economy.

Times like these can rattle even the most seasoned investor. So, what should you do if you are worried about your own retirement savings or other investments?

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STAY CALM

"The guidance for long-term investors remains intact — do not panic," said Greg McBride, chief financial analyst at Bankrate.com. "As the uncertainty persists, the market frenzy will continue, perhaps for weeks, perhaps for months. But long-term investors must think in terms of years or decades."

Investments in the stock market are usually done as part of a long-term plan. Any money you need in the next few years shouldn't be in stocks anyhow. So hold on tight and ride it out.

That is exactly what Kyle Levin, a 32-year old tax analyst in Brooklyn, plans to do. He considered selling some stocks before the market volatility, but decided against it.

"I'm most upset I didn't sell everything a month ago when I thought it would get bad," he said. Now he plans to ride it out.

Experts say this is the best route for most people who are holding stock for their long-term goals.

"Markets fall sharply, but can also rebound quickly. No one knows when that comes and you don't want to be sitting on the sidelines when that happens," McBride added.

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REMEMBER THE PLAN

If you are retired, or nearing retirement, this could be a particularly stressful time. It is a good idea to reach out to your financial adviser or investment firm for advice or reassurance.

Hopefully, you've already made a plan for retirement, and solid plans are built to withstand volatility. That means money needed in the next few years is already in non-stock holdings. But retirement is long, and retirees need money to potentially last more than 20 years — so those funds may be invested in stocks. While it's unnerving, experts say not to worry about those holdings just yet.

Andrew Crowell, vice chairman of wealth management at D.A. Davidson, said that he has heard from several retired clients who are feeling stressed, but he has been able to reassure them. One recently retired client, who is in his 70s, emailed late one night to "sell everything and go to cash." It was both ill advised and against company policy to do so, since it came by email.

Crowell followed up the next day and was able to reassure the client that his plan was still intact and built to last. The client had three years of anticipated living expenses out of the stock market in a reserve account. And his portfolio was generating about 70% of his annual living expenses through dividend and interest income, so his reserves were "replenishing" each year as well.

"Due to the frenetic news he was hearing, he had forgotten about these facts," Crowell said.

Crowell suggest that, while it's good to be informed, investors should unplug a bit too. Between the 24-hour news cycle, social media and more, people might fall prey to making hasty, emotional decisions.

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START SMALL

If you simply cannot sit still, contact your investment firm, seek some professional advice or take small steps to reassure yourself.

Fidelity Investments said it has had an increase in client inquiries. Melissa Ridolfi, vice president of retirement and college leadership at Fidelity, said that while it can be nerve-wracking, the most important thing someone can do is not panic.

Instead, she said it may be a good time to rebalance your portfolio to make sure you have right asset mix. Over time, particularly with the market run of the past decade, some investors may have more equities than they intended or simply may have too much of their portfolio in one part of the market. Make sure you hold a diverse set of assets and equities with exposure to different parts of the market — U.S. small- and large-caps, international stocks, investment-grade bonds — to help calibrate your portfolio to your age, risk tolerance and goals. Or consider investing in a target-date fund, which automatically adjusts as needed over time and may provide more peace of mind during periods of volatility.

Panicking and selling off can also cost you in fees, taxes and lost potential gains. Think of the people who sold off at the market's bottom during the Great Recession and missed out on some of the greatest gains of all time in the recovery that followed.

Some people may even see the fall as an opportunity to buy. Cameron Correa, 43, said he bought Apple after the crash in 2008 and has reaped the stock market benefit from that. And he invested in Target last week when markets began to slide, because the stock regularly pays out dividends. While the current decline is "super stressful" he feels confident that once the viral outbreak is under control that the market will bounce back.

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SAVE SOME

The one thing anyone can, and should do, to help truly protect themselves is build up their emergency savings.

It is important at any time, but more so during times of economic uncertainty, to have cash readily available. If someone is unable to work due to quarantine, reductions or other reasons — they will still need money to get by. If times are good, the savings will protect you and your budget from other bumps in the road too — think leaky roofs, blown out tires or hospital stays.

And if time is on your side, the market slide is not a reason to avoid saving for retirement.

Josh Shelton, in Medford, Oregon, recently graduated and started his first job as a sports reporter at a local TV station. He set up an appointment with a Fidelity financial adviser to start investing for the first time. He still plans to invest in a mutual fund.

"I think buying now will be a good long-term strategy for when the stock market eventually bounces back and my young age gives me that flexibility to wait it out," he said.