Worse thing people do in a downturn, lock in their loses only to get back in after it's back up or park their money in a 3% CD.. Think of all those who sold out after the MKT opened after 911? Guess what, the DOW went down to the 7000s-8000s. Last I looked today, about 12,700.
Over the long run, stay diversified, and above all, DON'T TRY TO TIME THE MARKET--EXPERTS ON WALL STREET CAN'T.