NEW YORK (CNN/Money) - In 1997, in the wake of the death of Diana, Princess of Wales, Britain ground to a halt. Thousands stood watching her funeral procession Sept. 6 from the streets, millions more watched on television. Even weeks afterwards a hush settled on the country.

That hush was measurable -- look back at the U.K. economic statistics from the period and you'll see a sharp decline. Now economists think that, as the United States pauses to remember Sept. 11, the economy could pause as well.

"A lot of businesses are going to slow," said Morgan Stanley economist Bill Sullivan. "There's going to be lost sales, lost revenues, lost activity."

For some industries the effects of the attack anniversary are direct. Airline travel on and around Sept. 11 looks like it will be even slower than analysts initially expected. Airlines have deeply discounted (or even given away) tickets for Sept. 11. Travel-related businesses, like hotels, will almost certainly suffer as well. Retailers are scaling back on promotions during the week. Meanwhile, many companies have decided not to run ads during the commemorative TV shows that day.

Less clear are the effects on broader consumption. On Sept. 11 itself the tone across the nation will almost certainly be sombre -- not many people will be heading out to stores, the movies or restaurants. Productivity in the workplace may also come down a notch.

"There's definitely going to be nervousness around the event and a kind of inertia," said Lehman Brothers economist Ethan Harris. "My wife has already asked me not to come into work that day."

But the things that people would have done will only be delayed, Harris suspects. It will be similar to what happens when a big snowstorm rips through the Northeast -- once everyone's dug themselves out it's off to the mall for a little catch-up shopping.

Even in the wake of Sept. 11 last year, after initially falling, consumer spending snapped back sharply. Sales were depressed in September, falling 2 percent, but surged back in October when they rose by 6.2 percent. This was more than just the usual snap-back, however -- patriotic buying on the part of some consumers and a live-for-today attitude on the part of others helped lift sales sharply.

We can't know how long and how much things will slow this year -- whether it will be a day or week -- and we can't know what sort of bounce the economy will have off that downturn. The danger is that, in an economy showing new signs of weakness, a September slowdown is enough to put things over the edge.

More likely, thinks Miller Tabak bond market strategist Tony Crescenzi, is that a September slowdown dupes some investors into thinking the economy is heading back into recession. They'll be surprised when things get back on track.

"I think there will be an anniversary effect," he said. "But it will also bring a little bit more of a sense of closure. The more distance we put between now and 9/11, the less of a pull it has."