There many things that can cause Bitcoin price to fall massively. Most times it couldn't be rumors or speculation which causes a lot of people to sell and this will eventually cause Bitcoin price to dip drastically. Sometimes when exchange has been hacked and huge amount of coins are sold, the market will crash and even other people who left their coins on different exchange will sell and the sell oder will be higher than the buy oder making it dip. Infact anything that creat panic in the market causing  people to sell more than buy, that will eventually make Bitcoin fall drastically.