I dont think so, if we look back at BTC charts a few years ago, it's noticeable that it usually fluctuates at the beginning of the year.

Probably this is the effect of holiday seasons all over the world, people tend to convert their BTC into their respective fiat money to buy valuables or services in establishments that doesn't accept BTC yet.

But in the past year, BTC gained so much popularity that it caught the eyes of the government and banks all over the world.

BTC will continue to be popularize and maybe in the near future banks and establishments will start to accept BTC as mode of payment to most commodities. If that happens, such fluctuations will be minimized or eliminated.

2018 has the most oppurtunities for BTC, so we cant say that its the downfall of BTC, its just getting started.