In the early stages of either, they can be very difficult to distinguish from each other.  However, I would argue that what we are in now did not come out of nowhere.  The market was simply going sideways for almost the entire year prior to breaking down.  Besides, nothing seems to happen slowly to the downside anymore.  Everybody has the information quickly and is looking to lock in profits.  

So, keep it simple, until you are sure about what is going on you keep your bets on the side of the larger trend (down) and you keep your timing shorter.  If it changes, you adjust.  What you can't do is make longer term bets against the trend.  You'll get burned and learn a lesson that you don't need to.