How to invest when stocks are sinking

March has been a dizzying month for US markets. The S&P 500 just posted two days of back-to-back gains, but the benchmark index is still down almost 5% this month.

​ March has been a dizzying month for US markets. The S&P 500 just posted two days of back-to-back gains, but the benchmark index is still down almost 5% this month. Read More Breaking News, Latest News and Videos | CNN