We have seen a number of dark days for stock markets all around the world in the past months. But how frightened should we be? Is the next Great Depression upon us? How can we distinguish a small crisis from a huge one? One way to deal with these questions and to calm our feelings of panic is to look closely at a single bad day. When we do that, the details can show us that the bigger picture may not be as bad as we fear, and, hopefully, quell our feelings of panic.

Let’s look back at September 29. On that day, the Dow Jones Industrial Average fell 7% and the S&P dropped by 8.8%. The Dow’s declines were the largest since the 9/11 attacks, and the S&P had its worst day since Black Monday in 1987. Media headlines included comparisons to the “Crash of 1929” and even “The Great Depression,” but, in spite of all of this, were things really as bad as they seemed?

The first thing to do when we have a horrible day like this is to look at as many of the details as you can. Now, when you do this you should expect some bad news. But the real insight will come when you compare the details of a single bad day to the details of an even worse day that history has proven to be a true market crash.

So let’s put September 29 into perspective.

Before the US stock markets opened on that morning, bad news was already spreading. The financial crisis had reached Europe. Governments were forced to bail out the Belgium bank Fortis, the U.K. nationalized mortgage lender Bradford & Bingley, and Germany’s Hype Real Estate Holding. At home, Wachovia announced that it was in talks with several firms to be sold. Wachovia, in fact, did not fail, but scared customers had pulled their funds after Washington Mutual’s collapse.

On the stock front, the bad news continued. Apple dropped more than 17% after a Morgan Stanley analyst cut her earnings estimate for the company. Since Apple is a central figure in the Nasdaq, the Nasdaq 100 Index fell 10.5%.

After the lunch break, stock traders learned than the House of Representatives rejected the Emergency Economic Stabilization Act, also called “the $700 Billion Bailout Plan.” Since many traders had expected it to pass, the markets reacted heavily, sending the major indices to their worst levels since 2004.

All of that combined made September 29 the worst day in the United States stock market since Black Monday in October of 1987. In fact, in terms of the absolute dollar market value wiped out, more than $1 trillion, Sept. 29, 2008, was the worst day on record.

Now, of course, being the worst day in 30 years is not good news. But how bad was it, really? When we compare September 29 to Black Monday and the Great Depression, we find that we should really keep our feelings of panic in check.

Consider these facts: on October 19th, 1987, “Black Monday,” the Dow Jones Industrial Average Index lost more than 22% in a single day. And the Great Depression following the market crash of 1929 was even worse.

When we compare the details, we start to get some perspective on our situation. In the crash of 1929, the Dow Jones Industrial Average plunged 40% in two months. On September 29, we were “only” down 22% for the whole year. Furthermore, in the 1930’s, more than 9,000 banks, yes, nine thousand, failed, compared with fewer than 20 in recent years. Furthermore, around 40% of all mortgages were delinquent by 1934 compared with 4% today.

No doubt, we are facing tough times. What we need now is leadership and a strong government that makes smart choices. But what we also need is some perspective on our situation. Panic is never productive, and it is especially dangerous when the situation is not yet as bad as it could be. Letting our emotions get the better of us will not help our situation. In fact, it may actually be the very thing that brings us toward the brink of a crash which we have so far been able to avoid.

Together we can overcome these challenges, so long as we stay soberly focused on the reality of our situation. A little bit of history can show us, not only some mistakes to avoid, but also that we have much to be thankful for when it comes to mistakes we have not yet made.