Following steep losses in China, U.S. stock markets were selling off early Monday at a pace that hasn’t been seen since the financial crisis.

At Monday’s open, the Dow Jones Industrial average was down more than 1,000 points — its worst start since the downturn — though losses leveled off by mid-morning. The daily volatility comes after stocks had their worst week in four years.

Ordinary investors watching the market may wonder about how much damage the rocky market might do to their 401(k). It’s impossible to know what will happen next, but fund managers and financial advisers say it’s generally a good time to find out where you stand and make sure you’re sticking to your long-term investing plans.

If you’ve strayed from your original plan, it might make sense to rebalance your portfolio. Here’s what you need to know:

–What is a correction? Should I be worried? A correction is the technical term for what happens when stock markets fall at least 10 percent below a recent high. A bear market is what happens when stocks are at least 20 percent below that peak. The Dow reached correction levels on Friday and the Standard & Poor’s 500 index temporarily entered correction territory Monday. These moments are fairly common: On average, U.S. stock markets have a 10 percent correction about every 20 months, as investment columnist Barry Ritholtz recently pointed out.

And not all corrections lead to bear markets, says Michael Mussio, managing director of FBB Capital Partners in Bethesda, Maryland. If anything, markets have been unusually calm over the past couple of years, he says. That can mean that when corrections do take place, they may happen more suddenly than they have in the past, Mussio says. The steepness of a market drop is not necessarily a sign of how long the decline will last, he says. “Investors shouldn’t let that send them into a panic,” he says.

–What should I be doing? It’s a good time to look at your portfolio to see where you are invested, advisers say. But don’t make any changes that would take you away from your long-term plan. Know how much of your portfolio is invested in stocks versus bonds. Because stock markets have been climbing higher for six years, some people might have more money in stocks than they intended to, says John Hailer, chief executive Officer of Natixis Global Asset Management. You should also find out how much of your portfolio is invested in U.S. equities, compared to stocks from emerging markets and Europe.

–Does this mean I should be selling stocks? If you find out your portfolio is out of whack, it can be a good time to come back to your long-term investing plans. For instance, if you’re nearing retirement and were planning to invest no more than 60 percent of your portfolio in stocks by this age, but find your exposure is now closer to 70 percent, it’s okay to scale back to your original goals. “You need to have portfolios matching up with your time horizon and your risk,” Hailer says.

But don’t rethink your entire plan because of today’s volatility. And if you’re still decades away from retirement or won’t need the money for a while, you can afford to keep the majority of your portfolio in stocks because you have time to recover any short-term losses. Keep in mind that people who cut down their stock exposure market during the downturn in 2008 would have missed out on more than six years of gains.

–Is it time to dump Chinese stocks? U.S. investors were spooked by a selloff in China that the media there is dubbing “Black Monday.” The turmoil there was sparked by growing concerns about a slowdown in the economy, so it might not be a great time to be upping your exposure to emerging market stocks, which are heavily influenced by what happens in China, Mussio says. Stick to the allocation you had originally aimed for, and if you’re not sure about where to invest, it might be better to stay closer to home, Hailer says. “The U.S. market is a great place to be,” Hailer says. “It’s holding up better than most global markets.”