If you look back historically, this is common early in the year. Employees with stock get vested (from 3 years ago) and take advantage by cashing out. You can put it in a mutual fund and earn a decent rate of return - better than the prospect of NVS stock longer term anyways.
I'll wait a bit before I cash mine out, there will be a run up in prices in February when they need to set the strike price of all the options they dole out (can you say manipulation? I knew that you could....) - that is typically the stock high point for the near term.