It's only because of the supply and demand of bitcoin in the market cap. This two component (demand and supply) have big effect on the ups and down of bitcoin price. Now bitcoin is falling it value because the demand is to low in the market cap also supply and volume of bitcoin now in the market cap is low. Then bitcoin change rate in 24 hours is 3.39%, this figure can affect the movement of bitcoin price within 24 hours weather its value is high or low. That why bitcoin value is changing time to time and hard to predict what will be happen to the value of it.