The key demand-side metrics indicative of that psychological shift, for Langan? "Oil, commodities, and the dollar," he said.

Oil, which, at $114 per barrel, has dropped more than $30 in about a month, and is behaving as if global growth will slow; commodities, in general, have retreated by more than 15%; and the dollar, driven lower for a decade by U.S. policy errors, is now rising and acting as if investors believe the U.S. economy will be the first to recover from sluggish economic conditions, Langan said.

The above describes global conditions that are pretty much the direct opposite of sentiment less than a quarter ago. But will the current sentiment/concern endure? Is it indicative of a trend? Langan says we won't know until we get Q3 GDP data from the U.K., Germany, and France in early October.

But if GDP does slow across the Atlantic, Langan said classic economic theory will have been vindicated. Among other points, the classic economists argued that at some point +$100 oil prices would slow global growth, and that, despite globalization and rise of Asia, an economic slowdown in the United States slows commerce just about everywhere, he said.

Economic Analysis: As is so often the case in the markets, it's amazing how quickly sentiment can change. In this case, from a world arguing that 'decoupling' exists (the world economy can grow without the U.S. economy growing) to a global slowdown exists (a U.S. slowdown presaged the global slowdown). The view from here is that oil must drop below $90 per barrel to take pressure off consumers' (and business executives') budgets, and provide some stimulus for ailing economies in the U.S., U.K., and Europe.