On Tuesday, the stock market gave up some of its recent gains, with a combination of economic worries and rising geopolitical tension holding back investors from pushing the market to further gains. By the close, the Dow and S&P 500 both fell between 0.75% and 1%, but for Twitter (NYSE:TWTR), athenahealth (NASDAQ:ATHN), and Capstone Turbine (NASDAQ:CPST), the losses were much more dramatic, sending shareholders scurrying for cover.

Source: Twitter.

Twitter plummeted 18%, adding further to its recent losses as the social-media stock hit a new all-time low. The post-IPO lockup period for insiders expired today, with the possibility that more than 80% of Twitter's outstanding shares could be sold at any time. Many prominent insiders have said that they plan not tell sell their Twitter shares, but with many investors questioning Twitter's ability to keep up its growth rate, nervous shareholders took the event as an excuse to get out. Bullish investors, on the other hand, should take comfort in the fact that lockup expirations associated with Twitter's main rival proved to be close to that stock's eventual lows from which it posted huge gains.

For athenahealth, today's decline of 14% came as Greenlight Capital hedge-fund manager David Einhorn announced that his firm had taken a short position in the cloud-based medical billing and clinical services company. Einhorn's case at the Sohn Investment Conference late yesterday characterized athenahealth as a "bubble stock" that would more accurately be seen as a business-services provider rather than a cloud-computing stock and said that the shares could lose 80% of their value. Given Einhorn's track record of making successful short calls, investors rushed for the exits even as the company and some analysts challenged Einhorn's thesis. More generally, Einhorn has said that he thinks that we're in a second tech bubble, and the reminder of that might have been responsible for sending the Nasdaq to bigger losses than the overall market today.

Source: Capstone Turbine.

Capstone Turbine plunged 15% as investors reacted to analysis of the company's preliminary results for its fiscal fourth quarter. The company made numerous disclosures in its prospectus for its most recent secondary stock offering, and analyst Adam Gefvert noted that the figures included the revelation that Capstone Turbine expects a sequential drop in revenue from the previous quarter as well as a lower than expected cash balance. With shareholders already on edge because of the offering itself, the suggestion that the microturbine-maker's recent encouraging results could simply be a flash in the pan raised new concerns about the sustainability of the stock's jump earlier this year.

Dan Caplinger doesn't own shares of the companies mentioned in this article. The Motley Fool recommends Twitter and athenahealth. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.