The Nasdaq is suffering from vertigo. The technology-heavy exchange's leading index has tumbled 6 percent in a month. Some leading Chinese internet stocks have fallen by much more. Deals are being delayed. In 2000, the reversal of the high-flying sector marked the beginning of a generalised correction and a downturn in the US and global economy. So far, the latest market downturn looks more like a warning of future trouble.
Tech is not in anything like the same sort of bubble now as in the 1990s. Some extreme valuation metrics have returned, but the Nasdaq's 150 percent rise in the past five years is nothing in comparison to the 10-fold one started two decades ago. And the current valuation of about 20 times earnings is half the 40 to which it rose late in 1999.
The soaring of the software and web industries is also symptomatic of other excesses. It could again be a tech loss of nerve that points down for other expensive assets. Even after suffering in the year since the US Federal Reserve first mentioned plans to scale back bond-buying, safe-haven debt issuance remains richly valued, with US 10-year yields well below 3 percent and Germany's below 2 percent.
And some markets previously seen as dangerous are now scaling new heights. Euro zone periphery bond yields are down to multi-year lows, as investors take courage from the European Central Bank's safety net of possible Outright Monetary Transactions and oxygen from new hints of quantitative easing.
A deep market slide may be avoided for now because only the Fed is starting to restrain itself. The Bank of Japan's massive money-printing continues and it looks entirely willing to do even more soon, if the increase in value-added tax depresses consumer demand.
Still, the Nasdaq's downward tilt is understandable and significant. Since the 2008 financial crisis, monetary policy has been far more successful at raising markets than at lifting growth or consumer price inflation. Equities, however, must ultimately stand on the solid ground of growth and earnings. Cheap money is more like easily shifted soil. Vertigo can cause things to spin out of control.