I think most people are selling their bitcoins as a reaction to the market, especially the ones who bought bitcoins when prices were low and are in good profit. It's quite possible that the initial dip on Sunday was due to few whales selling off their coins until August 1 and others are reacting to it by cashing out their coins. It's comparable to the situation when you bet $50 and it goes up to $200 then falls to $100 and you fear to loose it all.  

It was probably even worse that the dip started on Sunday (Weekend) and that probably didn't allow the price to stabilize and once it fell to a certain level then panic set in. If what I'm thinking is right we shall see an upward movement of price sometime later today or by tomorrow.