Panic selling is what draws the price of Bitcoin so down to the drain. Any event which leads to panic selling of Bitcoin can be considered as a contributing factor. The news of a hacked exchange site, false news from governments, banks and the media, a Bitcoin advocate country later banning Bitcoins etc. All these factors contribute to the fall in price of Bitcoin on the market.
While panic selling is without a doubt a contributing factor, most people do not begin to sell their bitcoin as soon as the price goes down, panic selling is the consequence of a huge dip in the market, then people get scared and finally they want to get out of the market regardless of the consequences.
Panic selling isnt the major factor on why bitcoins value is falling but rather that is because of manipulation cause by whales . they are the ones that have a large capital , thats why they were also the one that can easily turn the tides in their own favor .
Yet those are only few of the known factors on why btc is falling but overall we should not worry at all because no matter how low the price can get , there is always a chance that the value can go up and recover because that is the system on how cryptocurremcy works .