Stick with your plan would seem to be the best advice. Markets go up & markets go down and any long term plan should include both. But with the market down there are a couple of options to tweak your portfolio while sticking with your larger plan.
Two options were mentioned by our advisor to consider are *IIF* you have "cash" on hand that you don't need in the foreseeable future, (i.e. not your emergency funds, or balloon payment funds, etc.) First, go a little heavy in stocks because they will come back. (She is thinking next fall, but admits it could be five plus years.) Second, roll regular IRAs or 401K funds into Roth accounts. The value is depressed right now and (US!) tax rates are at recent lows, so you minimize the tax due and convert all future growth to tax free. Of course, YMMV and consult your own financial and tax advisers.