I believe that a correction has started. Please do not be fooled by people calling for a bounce! Yes the markets do appear to be over sold and may bounce but it will only take a day or two more of down side after a one or two day bounce to hit your account hard especially if you like to trade on margin. So where longs are concerned look to book profits more quickly (like at 2x risk instead of 3x risk) and try not to over night longs but if you must do so; use half positions or less. Gap downs like today are often accompanied by friends, so be careful on the long side!
Good luck and good trading!