You may notice that there's a bit of a pattern happening here. Every 41 bars or so (about every 3.4 years) there is a significant dip in the price, most prominent among those of course are the January 2015 and August 2011 massive falls that caught many traders by surprise.
The intervals are eerily similar as we already mentioned, about 1250 days apart. So just for fun, when could the next drop be? June 2018. Not sure who would hold a position for a couple more years (unless they have uncharted patience and no rollover fees). Nevertheless it will be interesting to see how it plays out.