Bitcoin dumping is the main reason we see bitcoin Going 1000 dollars up and down in a day. Bitcoin dumping is done by the the big people having lakhs of bitcoin. They dump 1lakh or more bitcoin in a day at higher price and after dumping price comes down and panic selling gets started among the small investors or beginners
So as in chart we can clearly see in red circle how bitcoin got dumped
So these big people called whales dump their bitcoin at high prices and then buy again at low price
And the other big factor is news, whenever a news a being circulated on internet about bitcoin. If the news I bad then again panic selling starts and if it's good buying starts
From @govind99