Consumers may think it’s whiplash, but it’s really deflation.

Gas topped $4 a gallon in July at the same time agricultural commodities were hitting record highs, pushing food prices through the roof.

The Federal Reserve abruptly -- and temporarily -- halted a series of interest-rate cuts citing the fear of inflation.

But all that’s changed. The average price of a gallon of gasoline in the U.S. has plummeted to $2.07 and other key staples have followed suit.

Now it’s all about deflation.

“Deflation is when prices are falling, and not just on a few items, but broadly across the economy,” said Gus Faucher, director of macroeconomics at Moody’s Economy.com.

Consider that the Consumer Price Index, the country’s most closely watched inflation barometer, dropped 1% in October, the biggest monthly decline since the government started keeping records in 1947.

Many analysts expect another drop for November.

That’s a startling about-face from as recently as June, when consumer prices spiked 1.1%, the second-fastest pace in a quarter-century.

How is this a bad thing?

For starters, it gives consumers and businesses an incentive not to buy now -- but rather wait until later when, presumably, prices will fall even further.

“That means if you’re in a period of weak demand, that demand is going to get even weaker,” Faucher explained.

Consider the auto industry, for instance. Car dealers have slashed their prices in an effort to move cars -- gas guzzling SUVs and pickup trucks, in particular -- that are piling up on lots across the country.

But many consumers are apparently holding off, waiting for an even better deal.

Apply that dynamic to all sectors of the U.S. economy -- most notably, perhaps, the housing sector -- and there are all the makings of a deep recession.

Another downside of deflation, according to Faucher, is that it complicates the Fed’s job of setting interest-rate policy, which tends to target inflation rather than deflation.

“It makes the Fed’s job much more difficult, but they’re very aware of this and they want to make sure deflation doesn’t happen. It happened in Japan in the early 1990s, and it contributed to [that country’s] lost decade,” he said.

Indeed, economists believe the Fed is prepared to take drastic measures to prevent prices from falling to dangerous levels.

JPMorgan economist Michael Feroli wrote in a recent note to investors that the Fed will probably slash interest rates to zero by cutting 50 basis points from key rates at each of its next two meetings on Dec. 16 and Jan. 28.

That would essentially make it free to borrow money, a move that would hopefully give a powerful boost to an economy sliding into recession.