the fluctuation of bitcoin value is very unexpected, we can not predict the movement of bitcoin values according to our expectations, it all depends on the market and how much supply and demand occurs on each market of digital currency itself, so we do have to do daily analysis before we wish to investment on bitcoin with a lot of money.
It's becoming more and more like stock market, where big traders can bring the value up and down, isn't it? Anyway, as cap keeps growing it's gonna be harder and harder for them to affect the price so I guess we shall see more stability in the future.