Everything's correlated to the yen right now. I'll get some of the specifics here wrong but my understanding is: When the yen suddenly strengthened (blue line going down on the chart), the many entities shorting the yen in one form or another (e.g. the yen carry trade) had to scramble to cover their shorts, so they sold whatever they could, and bitcoin's easy to sell.

Everything's correlated in a panic, but I'm curious how long this will remain the case.