Day of reckoning
But it's as well to remember that they are the symptom of the disease, not the disease itself.
The underlying illness remains in the financial system, as manifested in the record amounts banks were charging each other yesterday for lending to each other for three months.
One serious anxiety concerns the auction today to settle liabilities on insurance - or credit default swaps - on debt of the collapsed investment bank, Lehman Brothers.
As I noted a couple of weeks ago, there are estimates that claims under insurance contracts will total $400bn. Sandy Chen of Panmure was one of the first to highlight the scale of this looming problem.
If demands for payment are as big as $400bn, there will be pain for banks, insurers, hedge funds and other financial institutions.
For every winner in a claim, there is a loser, the underwriter who has to divvy up. And if the underwriter lacks the resources to pay - which may turn out to be the case in this under-regulated market - that creates two losers: viz the bust underwriter and the claimant which doesn't get the money on which it was counting.
And if that claimant had been calculating its own financial strength on the basis that it had insurance against its Lehman debt, well then failure to receive payment could shatter the integrity of its balance sheet. Which in turn would create potential losers among its creditors.
So this day of reckoning on Lehman credit default swaps is momentous - and it could not come at a worse time for fragile bank shares.
The fall in Morgan Stanley's share price yesterday was a remarkable 26%, on the back of various nebulous rumours and as Moody's said it was reviewing Morgan Stanley's credit rating for possible downgrade.
There was also a doubling in the credit-default-swap price for insuring Morgan Stanley's debt: there was contagion from this opaque market to the more transparent stock market.
As soon as regulators have time for breath, they surely must as a matter of urgency bring some light, order and proper regulatory oversight into the credit-default-swaps market
But probably more urgent is for the US Treasury Secretary to decide how and whether he will inject US taxpayers' money into banks to recapitalise and strengthen them, along the lines of what the British Treasury is proposing to do.
But he "only" has $700bn to play with, which no longer looks that enormous in the context of the $400bn claims that may be enforced in just the next, anxiety-inducing few hours.