From January 2017 to March 2018, there has been a fairly reliable 2-month low-low sequential cycle. If this cycle holds this time it will occur about May 19th.
During the 2017 run up, it timed major lows as well, but on the way down (since the December 2017 peak) it is missing the major lows and timing secondary lows.
On the long term chart it looks like just a blip, but 4 years ago, BTC experienced the most similar percentage rise and fall to one we just had from December 2017 to today.
An overlay of the two periods exactly 4 years apart shows some interesting similarities in not only percentage change, but volatility, magnitude, direction, duration, and time of year.