Regardless of when or if, one should make a plan prior to the drop. Decide what will be sold or held through the bottom of the stock market(or whatever you fear) BEFORE it happens.. In addition You don't want to be out of the market completely because most big gains happen after these big crashes. If you get out then you wreck your future retirement savings because you've just locked in your losses of 20-60%(below 20 is just a correction)