The S&P 500 Index (SNPINDEX:^GSPC) needed to take a break. It had hit all-time highs in nine of the last 10 sessions and, on Thursday, the index did something unconventional: It took a step back. Perhaps it was warranted, as new housing starts slipped big-time in April (more than 16%), and recent industrial production figures underwhelmed. But while the S&P was going through a modest, eight point, 0.5% pullback to close at 1,650, the following three stocks were suffering through far more severe sell-offs.

Chip maker Advanced Micro Devices (NASDAQ:AMD), which has been on an absolutely unbelievable run as shares soared more than 80% this year, cratered 12.6% today on some scathing comments from a Goldman Sachs analyst, who thinks the run-up has been exaggerated. He noted that, while AMD doesn't traffic exclusively in the PC market, the PC segment still makes up 45% of the company's sales, implying that investors have gotten too excited about AMD's involvement with the new Microsoft Xbox consoles. 

Biotech company Celgene (NASDAQ:CELG) is the second-largest decliner in the index today, slumping 4.7%. The company develops products that treat cancer, including multiple myeloma drug Revlimid, which reportedly achieved a response rate of 56% in a new clinical trial. The counterintuitive fall in Celgene today comes after a Piper Jaffray analyst lauded the results of the study; obviously, not everyone agreed with that sentiment. 

Lastly, Computer Sciences (NYSE:CSC) logs its second consecutive day on this list, shedding 4.7% on the heels of its quarterly earnings announcement. Sometimes, there's little rhyme or reason behind a stock that continues to fall and fall, other than momentum. That may very well be the case with Computer Sciences, which, as a leader in the IT field, not only was more profitable in the most recent quarter, but also returned more than $250 million to shareholders through share buybacks and dividends.