Bitcoin is somewhat stable but not for more than a week. The current price fluctuation is a result of panic selling and smart investing from the investors. We have seen a huge price rally in the last quarter of the last year and now the correction is taking place so we are in the turbulence phase and I don't see any reason to worry considering the long term.
That is the definition of begin unstable don't you think, after all if the price of bitcoin keeps moving every week and it does in such a big way then we cannot really say bitcoin is stable at all but this is not going to change in a long time so if we want to invest in bitcoin we need to get used to it.