Its all about supply and demand.
When the demand for bitcoins is less the price falls and when the demand for bitcoin is more, the price for bitcoins rises.
There are tons of buyers who sell on huge amount and when the price falls they then buy again at a low price.
These are times for us to buy and make a profit.
I too just bought 0.5btc more for investment... its not everyday that the price falls at a huge margin.