The Rewarding Distibution of US Stock Market Returns
The UP years have occurred more frequently than the DOWN years and that may be one reason that "down" years stand out so much even when they are expected. When things happen with less frequency (like actual down years) they make much more noise and can be very unsettling.
Keeping a long-term perspective is hard to do, but if you can with the help of your financial advisor you will likely be rewarded.