This is due 1 reason, Whales, people with a boatload of BTC.
They are creating huge sell walls(putting millions on a sell order), so everyone would have to sell for lower => price drops.
Whales pick up the BTC for a penny and remove their insane sell walls => price goes back up.
If you look at the chart of 12-15 hours ago as of this post, you can see the example ;)