Looking at the above chart, which displays the bitcoin price from the low just under 200$, and following a so-called objective Elliott Wave counting technique, I come to the conclusion that a new top is likely, but after that a serious correction must follow. We can correct to 2000$, but also to 1000$. This will not harm the long term uptrend.
Zooming in on the last leg up from July 16 using a shorter (3 hour) time frame, it shows we are are in an impulse up, with wave 5 (this is the last wave of an uptrend) possibly already in the making and ending soon. Although it must be said that waves can extend, meaning they subdivide in 5 waves of lesser degree. In any case you should be expecting a new all time high which I expect to be the last top for some time to come. Especially taking into account the divergence in the Elliott Oscillator which is a sign that the uptrend is losing strength.
On a more fundamental note, I would say this makes sense, now that all the excitement regarding SegWit has ended. Buy the rumor, sell the fact. Also, after a bull run this spectacular, and for more than 2 years, a correction is overdue, healthy and must follow.
Normally when bitcoin goes down, altcoins follow. I have personally sold all my altcoins, will hold only bitcoin, litecoin and IOTA and add to my positions as the correction unfolds.