It was like a Wall Street version of one of those Keystone Cops comedies of the 1930s, but at least one investor wasn’t laughing. According to his stockbroker, he almost had a heart attack as a result of what appeared to be an enormous plunge Thursday in after-hours trading in the price of the high-flying shares of Internet search engine Google.

The incident, which some Street pros contend is a blunder of major proportions by Nasdaq, surprisingly managed to escape the eyes of the financial press and was never reported even though the decline — an astonishing drop of nearly $350 a share in a mere 10 minutes — was the greatest ever in the history of the stock market in after-hours trading — and undoubtedly in regular trading, as well.

Here’s what happened. On Thursday, trading in Google wrapped up the day at $387.12 a share at the usual closing time of 4 p.m. A minute after the close, Google announced its second-quarter results: better than expected earnings, but decelerating revenue growth from the prior quarter.

At 4:02 p.m., in after-hours trading, Google’s shares got creamed, initially tumbling to as low as $364, down more than $23 a share from its close, but then rallying back to $391, for a gain of nearly $14.

At about the $391 price point, an order originated on Instinet-ATS (a Nasdaq company) that triggered trades between 4:10 p.m. and 4:12 p.m. at a price as low as $38 (representing a drop of almost $350 a share from the close). In brief, someone from a Nasdaq member firm punched in an erroneous figure to commence a trade.

That led to a host of subsequent trading at $38, as well as at $37.81, $37.82, $37.99, $38.02, $38.03, and $38.05.

Nasdaq, and perhaps the Securities and Exchange Commission, will almost certainly look deeply into the situation to make certain there was no hanky-panky. But that’s little solace to the investor I mentioned earlier. He had bought 200 shares earlier last week at around $380, or about $76,000, only to discover from his broker he was suddenly sitting with a fast and damaging paper loss (at the quoted $38 a share) of about $68,400.

The broker told his customer the $38 price was probably a mistake, but he added that he could not guarantee it, given the volatility in Google’s shares. Nonetheless, the customer, he said, became hysterical, complaining of chest pains and crying. “The way he sounded, I thought for sure the man was going to have a heart attack,” he said.

Nasdaq has a “clearly erroneous transaction” rule under which at some point the exchange will inform its members of an incorrect price. But in the case of Google’s collapsing stock price, it didn’t disclose to its members until 4.22 p.m. on its NasdasqTrader.com Web site that it was looking into the matter. What’s more, it took Nasdaq until 5:01 p.m. — more than an hour after the close of regular trading — to finally disseminate the news of its decision to cancel all after-hours trades in Google that were at or below $352.07, which is roughly 10% lower than its closing price. Further, Nasdaq said its decision was not appealable.

One market maker laced into Nasdaq for waiting so long to cancel all trades below $352.07. He noted, for example, that customers or broker-dealers that purchased stock at levels that may not have immediately been perceived as erroneous could have been caught with substantial losses if they sold their stock before the 5:01 p.m. announcement. For instance, anyone purchasing stock between $300 and $352 (about 52,000 shares) also had their trades cancelled.

Of course, for those investors who put in orders to buy the stock at the $38 level in after-hours trading, it was like discovering the pot of gold at the end of the rainbow. Alas, due to the trading fiasco, it turned out to be fool’s gold.

Google could not be reached for comment over the weekend. One money manager told me he spoke to a management contact there and found great criticism of Nasdaq, a feeling that it was asleep at the wheel for not issuing a public statement, as it obviously knew the $38 quoted price was not real.

Nasdaq strongly defended its actions, with a spokeswoman telling me it typically takes an hour to break trades, given the need to exercise caution in such situations and to make certain all parties are notified.

So where does Google’s stock, which closed Friday at $388.12, go from here? One of Wall Street’s leading Internet analysts, Morgan Stanley’s Mary Meeker, figures it’s on the way up. In a recent commentary to clients, she described the company’s second-quarter results as “solid, not great.” But her 10-year discounted cash flow model values Google at $500, while her discounted price-to-earnings valuation pegs the stock in a $545–$719 range.