you are describing panic selling yourself!
when such thing happens usually weak hands (newbies) start selling as soon as they see price going down then it starts a chain of events which leads to more sells.
but the effect depends on the cause of the panic sell and it is usually small and at worst case scenario it is only $50 reduction of price.
It's so pathetic to panic selling while bitcoin is strong cryptocurrency even there are some bad news about it.
Bitcoin always recover the price like 200 times when it falls due to many accidents.
The fact is, mostly people buy bitcoin with intended to sell it out when the price reach certain point.