As the nation watched the stock market plummet yesterday, some saw it as a great opportunity. The plunger didn't surprise financial planner Don Reiman. Contrary to some who blame the debt ceiling bill, Reiman says the real culprit is concern that we could be headed for a recession.   As for your 401k's Reiman says the best thing to do is actually increase what your saving in your 401K plan. Those same stocks you were buying for the last few months are a lot cheaper now so the money you invest today will be buying more shares. When the market comes back  Reiman says that will make you more money than if the market just stayed level or went up a little bit every day.