After a week that saw markets up 300 points and then down 800, is it time for ordinary investors to consider their best course of action? Shift from stocks to bonds? Move from index funds to money markets? Take out cash and stuff it under the mattress?

The answer, experts tell NBC News, is to not lose your head, and remember that discipline always pays off better than panic.

Chances of a recession

Much of the movement has been market concerns over the trade war between the U.S. and China and the impact on local and global economies. When it looked as though there was a deal, share prices shot up. They then dropped when no one in either country could explain exactly what happened.

But that is temporary volatility, a condition that has become a regular occurrence this year.

"Right now I think the volatility levels are well up into the [20 percent range]," said Chester Spatt, a professor of finance at Carnegie Mellon University's Tepper School of Business. Typical for a year would be about 15 percent. The 10 percent we saw in 2017 was "abnormally low."

The big question is what will happen next year. Some think a recession is likely. "One of the best indicators if we're going into a recession has been flashing lately," said Glen Smith, managing partner at Glen D. Smith and Associates.

He's referring to the so-called inverted yield curve, when the interest on a short-term Treasury bond is higher than on a long-term one. It indicates that people are more uncertain about the future. An inverted yield curve has also frequently come before a recession.

Yet some experts think worry at the moment is overblown. According to Joe Mallen, chief investment officer at Helios Quantitative Research, there have been only 9 times since 1950 that the S&P 500 dropped by about 10 percent. "Remarkably, it only took an average of 35 days for the market to recover the lost ground," he said. "In one case, a full recovery happened within only 16 days."

Rebalance your portfolio

That isn't to say you shouldn't be concerned — just measured. There is a reason that the experience starting in December 2007 was called the Great Recession. It was unprecedented except for the Great Depression. Downturns are common and generally aren't so devastating. Instead, use the current circumstance as a prod to reexamine your portfolio.

"I would focus on having an asset allocation [across stocks, bonds, and other investment vehicles] you're comfortable with over the long run and perhaps getting there relatively quickly," said Spatt. If there is trouble, best for it to arrive only when you're ready. Look at the types of risk you can manage and consider how soon you might need your money. If retirement is near, for example, lower-risk and safer investments might be wise.

Work with a professional who might know more options available to you. There are types of annuities that can safeguard your principle and still give some potential for gains, says Mark Charnet, chief executive officer of American Prosperity Group. "If I could buy an investment that has an opportunity to go up in the market but zero participation in the downside, that should have everyone's name on it" who needs more stable investments, Charnet said.

And be sure to check the details of the investments you do have. Trader and co-host of the podcast BailStreet, Danny Moses, who was featured in "The Big Short," said exchange traded funds, or ETFs, are misunderstood by many who have them.

Although they are frequently presented as index funds, "they're [often] very weighted toward the largest market cap companies," Moses told NBC News. Because trading is computerized and automated and many of the ETFs in a given market sector will have a lot of overlap in stocks they own, they can feel even more volatility. "No one knows what they own and there's a generally false sense of security by owning an ETF," he said.

So, take a deep breath, look at the details of your portfolio, rebalance as you need to, get some good advice, and then don't obsess over what you can't control.