Stock market fever is back, and that's always a good reason to worry. Lately there has been a spate of headlines with titles like, "Is this the beginning of the next great bull market?" and "How to play the melt-up in stocks." The stock market got 2013 off to a strong start with a nice gain in January, and excitement about equities has been building. However, before you rush headlong into the market, here are four things to think about.