Stocks posted sharp losses on Thursday, adding to declines earlier in the week, and sending the Dow down another 255 points. A combination of factors helped send shares lower, including slumping energy prices, worries about the health of financial stocks in Europe, and overall uncertainty about whether an official bear market is inevitable after the seven years of strong gains that the stock market has seen. Some big-name stocks also posted extensive declines, adding to negative sentiment. Among them were Bank of America (BAC -1.54%), Boeing (BA -2.20%), and Zynga (ZNGA).

Bank of America fell 7%, partially in response to concerns about its European bank counterparts. Bank of America has been under pressure for some time due to worries about the state of the Chinese economy, as well as the bank's small, but not insignificant, lending exposure to the hard-hit energy sector. Europe's woes upped the ante for the big U.S. bank by reawakening fears of systemic risks to the global banking system.

The turmoil worldwide has led most market participants to expect less-dramatic policy moves from the Federal Reserve, and the decline in long-term rates that has accompanied projections for a weaker economy has flattened the yield curve, and could potentially cut B of A's future profits. Until energy prices bottom out and the fallout works its way through the financial system, Bank of America will likely continue to suffer from uncertainty about its future.

Boeing also dropped 7%, but recovered from double-digit percentage losses after the SEC announced an investigation into how the aerospace giant reported sales and expenses related to a couple of popular aircraft models, including the iconic 747 wide-body commercial jet and the newer 787 Dreamliner. The biggest problem that Boeing has with its accounting is that its aircraft development and sales programs play out over decades, so the company has to figure out how to account properly for the money it spends developing the aircraft, as well as the revenue it generates from selling the planes.

Given how insignificant a three-month period is in the context of such a long lifespan for a typical Boeing jet, judgment calls can lead to big impacts on a quarter-by-quarter basis. What the SEC will determine is whether Boeing misled investors by making its results look more favorable than it should have, and many investors saw the investigation as a good time to sell.

Finally, Zynga plunged 15%. In its fourth-quarter earnings report on Wednesday afternoon, the mobile-game specialist posted disappointing metrics, including average daily and monthly active users, and the number of players who pay for access. The company managed a break-even performance on the bottom line, and revenue was higher than expected, but Zynga said that its first-quarter results would likely be weaker than what investors had forecast. The game maker also announced an acquisition; but at this point, Zynga stock has fallen so far, that many investors are starting to give up on the company's chances of ever making a full recovery from current levels.