Don't panic.
The market has been oscillating between 13,000 and 14,000 for months now.
A rule of thumb: Stocks are a long-term investment.
If you are young, a lot of your retirement account should be in stocks--well diversified, preferably in mutual funds.
On the other hand, if you are close to retirement, your money should mostly be in other things. Whoever's holding your retirement accounts should have advice on this.