As long as you have invested intelligently, this is no problem.
If you are young (assuming the financial system or society in general for that matter doesn't completely collapse) the market will recover and this will be a distant memory in 30 years when you begin tap into your 401k. In fact, this is a great time to start buying. Stocks could and probably will continue to go down, but as long as you have the means to buy stocks now and sit on them for a few years, you will see good returns eventually (again assuming we don't experience a total collapse, but in that case it won't matter where you have your money anyways)
If you were close to retirement and you still had a large proportion of your savings in stocks, mutual funds, ETFs, or even indexes, you can only blame yourself for what you lost.