If you’re a seasoned investor, you shouldn’t be worried; For those experiencing something like this for the first time, here’s something from the book that Warren Buffett calls ‘one of the best investing books of all time’:

The true investor scarcely ever is forced to sell his shares, and at all other times he is free to disregard the current price quotation. He need pay attention to it and act upon it only to the extent that it suits his book, and no more. Thus the investor who permits himself to be stampeded or unduly worried by unjustified market declines in his holdings is perversely transforming his basic advantage into a basic disadvantage.

– Benjamin Graham,  The  Intelligent Investor