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You have what is called unrealized losses. What this means is if you sell now you will lose the money. If you hold it - well, it has a chance to go back up and even higher.
Considering you said you have 25 years until retirement, you may want to consider staying invested in some of your holdings.
Also, right now is a good time to invest. This may be a hard thing to hear after seeing your total value drop by thousands, but you are buying at a relative discount.
For example, look into an index linked product for long term. Most indexes have dropped significantly in the last couple months (around 30%).
As well, as jittery as you are - keep in mind that keeping your money under a matress is the last thing you want to do. At the very least put it into a holding that will yeild small but stable returns. A GIC or money market fund would suffice.