Looking at other tech stocks this seems like more of a broader downturn today. Twitter was down 7%, Zynga was down 4%, Amazon was down 3%. Correlation ≠ causation. I'm not buying the drop is from the Oculus buyout.
After a quick google it seems Facebook's beta is ~2. So a NASDAQ fall of <3.5% is an indication that something other than a general downturn impacted Facebook's price
Please correct me if my understanding is wrong
There are much better guides to stock volatility such as the put-call ratio, implied volatility of options or general market volatility as measured by VIX.