Stocks: 'September slump' strikes again

september stock slump

If you are one of the 50% of Americans who have money in the stock market, you probably wanted to reach for Benadryl at some point this month.

The "September stock slump" came back with a vengeance in 2014. The S&P 500 finished the month down over 1.5%, its worst performance since January. The Nasdaq -- the main gauge of tech and biotech stocks -- lost 1.9%. Even the Dow, the index that tracks America's large and well established companies, ended slightly in the red, down 0.3%.

How did things unravel?

It's a valid question to ask. There was so much excitement in September, what with Alibaba (BABA) becoming the largest initial public offering in history, and the S&P 500 and Dow actually setting records. Then things turned sour.

Starting on Monday, September 22, investors hit the pause button and kept hitting it for much of the rest of the month. There were concerns again about how fast the Federal Reserve would raise interest rates. Would it move before next summer when most people expect it to take action? Fed chair Janet Yellen tried to soothe the markets, but the second guessing is back.

Related: Thank Janet Yellen or not?

Traders were also alarmed by a so-called "death cross" among small and mid-cap stocks that make up the Russell 2000 index. That's a technical term for when the 50-day moving average for an index falls below the 200-day average. In other words, the trend is down.

There's a clear polarization emerging again in the market where larger, more established companies are going strong and smaller, riskier ones are faltering. It was an excellent month for companies such as Nike (NKE) (up 13.5%), DuPont (DD) (up 8.6%) and Clorox (CLX) (up 8.4%).

So was September just a blip in an otherwise upward trend or is this a turning point? It depends on your perspective.

The pessimist's case: The bears of the investment world see stocks that are expensive and a market overdue for a correction. This is already the fourth longest bull market since 1928, according to Bespoke Investment Group, and we haven't had a true correction where the market dips 10% or more since 2011.

"We've had one record after another on the Dow and the S&P and yet the underlying economic and geopolitical fundamentals are still worrisome," well known investor Mohamed El-Erian told CNN last week.

Layer on top of that concerns about the Federal Reserve raising interest rates, a flat-lining European economy and ongoing strife in many parts of the world from Ukraine to the places ISIS is terrorizing in the Middle East. Furthermore, there's a case to be made that many companies have been boosting their bottom lines by cost cuts, not genuine growth and innovation for the future.

Related: Is it time for Wall Street to issue a correction?

The optimist's case: Most investment strategists that CNNMoney hears from are sticking with U.S. stocks. They believe the slow, but steady growth will continue. Consider this: despite the lackluster September, the S&P 500 is still up 6.7% for the year.

Optimists see an economy that is getting gradually better with manufacturing and employment picking up, among other positive signs. For example, FedEx (FDX) was one of the best performing stocks in September. The company is often seen as a beacon of corporate health.

They also see companies with a lot of cash. Even if there are headwinds, they're a lot easier to deal with when you have a rainy day fund. Corporate cash and short-term investments (some companies temporarily invest their cash to get a little extra bang for their buck) are near all-time highs, according to FactSet.

"We don't go into bear markets because stocks are too expensive. Typically, it's because of a policy error by the Fed or government," reminds Robert Landry, a fund manager for USAA.

The market always has bumps in the road, even during a bull run.

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