Why are people nervous about the Stock Market?

Let me show you a graph of the S&P 500 and the High Yield bonds or HY. High yield bonds are no better than BBB; otherwise they are not the most secure bonds. We have a drop in High Yield bonds because the Market demands higher rates from them, so the value of the bond goes down. See it? At the top is what is happening now and the bottom is what happened in 2007-2008.