There's a first time for everything, and one of those times came Thursday for Richardson financial planner Sandra Strohmeyer.

"Today was the first day I heard someone say, 'Sell it all!' " she said, referring to a call she got from one couple.

Dumping stock Thursday would mean bailing out after some of the most dramatic market declines in decades, Ms. Strohmeyer knew, locking in their recent losses and going against that great rule of investing: Buy low, sell high.

So Ms. Strohmeyer, who works at Ameriprise Financial Inc., tried to talk her clients out of taking the drastic step, telling them to think it over and call back before the market close if they didn't change their minds.

"They still sold. That is an extreme panic," she said.

Panic and fear abounded Thursday after seven straight days of deep losses in the U.S. stock market. One leading index, the Dow Jones industrial average, has fallen 21 percent since Sept. 30. It's down 35 percent since the beginning of the year and off 39 percent from its all-time peak on Oct. 9, 2007.

Meanwhile, the Standard & Poor's 500 index and the Nasdaq stock exchange have each plummeted about 38 percent so far this year, and about 42 percent compared with their October 2007 highs.

"This is one of the deepest bear market troughs that we've experienced since World War II," said Russ Labrasca, executive vice president at Wells Fargo Private Bank in Plano. "Bear markets are sharp, fast and exceedingly painful."

Ms. Strohmeyer's clients who sold their shares had suffered a relatively mild 18 percent loss over the past 12 months and already had 65 percent of their money invested in cash and bonds – hardly the riskiest of portfolios.

But "they're close to retirement. They're afraid," she said. "It's a shock. It's just happened so fast."

The current upheaval marks the second time stocks have been mauled in a bear market in the last 10 years, with this fall's damage coming about eight years after the tech bust began.

Financial planners say selling into the maelstrom doesn't make sense for most people.

"I would be a failure as an adviser if that happens," said Bob Stowe of Stowe Financial Planning LLC in Plano.

That's because the stock market is apt to bounce back in the long term.

Alas, there's no telling when that might be. It took more than six years for the Dow to climb back to its January 2000 peak.

Meanwhile, free falling into the downdraft is gut-wrenching.

"People are anxious at this moment," said Craig Rogers, president and chief operating officer of Rogers Capital Management Inc. in Fort Worth. "We all are."

The key is to focus on your long-term goals, Mr. Rogers said.

"Markets are very resilient," he added. "We know there are going to be bad times in these [investment] plans. We understand that, and I think our clients do, too. Those times are not fun, but they're not unexpected."

They also don't tend to last forever – at least not since the Great Depression that followed the market crash of 1929. (It did take the Dow 25 years to recover to its Sept. 1929 level.)

Most economists say a U.S. recession is likely, but a devastating depression like the one in the 1930s is highly unlikely.

If they're right, there may soon come a time when investors are clamoring to buy as stocks rise again.

"For investors with a long time horizon, a period of fear can also hold the greatest opportunities for the future," said Mr. Labrasca. "When the pain becomes this intense, it begins to truly feel like we're finding the bottom of this bear market."

Ms. Strohmeyer, the financial planner who heard "sell it all!" from one customer, said she had another client who seemed to follow Mr. Labrasca's logic. He called because he wanted to start buying.