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Keep breathing. You're fine. You'll be fine. You had paper gains. Now you have paper losses. Nothing is real until it's time to cash out and go home. (BTW, I'm down 27% for the year. I feel your pain when I look at my statements.)
Everybody's retirement accounts are down right now. If you're 65 and retiring in two years, that's a bit of a problem. If you're 42 and retiring in 25 years, it's not a problem.
Do not stop what you're doing. Now is the time to stay the course. There's a strategy called "dollar cost averaging" for retirement accounts. You buy invest the same amount when the market is going up and when the market is going down. Your expensive purchases (when the market is going up) will balance out your cheap purchases (when the market is down), and you'll create a reasonable average purchase price. IF you have a bit extra to spend during a down market, you can improve your average price by buying more when the market is down.
Typically, when the market rebounds it recovers 80% of the value it lost in a couple of months. So... if you just wait, it will get a bit better.
Do not try to time the market. Study after study shows that even professionals do poorly when they're trying to time the market. Amateurs get creamed. Get a sound, market based investment strategy and follow it.
You should check your investment strategy to make sure it's balanced and appropriate for your age. If you are unsure about doing this, various investment groups, like Vanguard, have "target retirement funds" that will balance these issues for you and automatically rebalance your portfolio as you approach retirement. You pick a target retirement fund based on your intended year of retirement. (Target Retirement Fund 2035 is for people whose retirement date is the year 2035 or thereabouts.)