In my opinion, the most noticeable effect on the drop in the price of bitcoin is caused by negative news about the crypto currency. Bitcoin reacts very sensitively to such news, because this changes the ratio between demand and supply, and it depends entirely on them. Recently, we could see this clearly when the bitcoin course reacted sharply with its fall to negative news from China, South Korea, India and other countries.
I think with low supply and high demand means price increases, but if supply is more than demand then it triggers the price to fall. And I think the bitcoin value is based on market supply and demand
There are many influential factor that triggers bitcoin prices to fall down. To name the most influential,the rule of demand and supply contribute to the price dump especially when a lot bitcoin users is selling out of panic.