Top technician: Yes, 2013 does look like 1987
Of all the periods that Worth looked at, 1987 is "the one that's the most correlated" with the current market—"it's running at a 96 percent correlation," he said.
Given that in 1987, the S&P fell some 40 percent in three months, Worth finds this correlation very troubling.
"Does it have to play out that way? No," he said. "But it really does speak to: What is one playing for by staying long? Is it asymmetrical risk-reward?"
In Worth's view, the risk-reward is indeed highly skewed. "Upside is limited, and by staying in, you embrace or prospectively take the punishment that is coming," he concluded.
(Read more: Siegel: Keep buying—you 'can't lose')
Dan Nathan of RiskReversal.com is of the same mind. "You probably have a few percent to the upside, but you could potentially have a really sharp down-10-percent move," Nathan said.
Of course, given what the market did in 1987 after topping out, perhaps a decline of just 10 percent would leave some investors thankful.