It's the bubble popping.. look through my posts, I predicted this a month or two ago.
A bunch of people rushed in, all not wanting to miss out on the next big thing and they worried that BTSX would go higher than Ripple and they panic bought.. only now everyone who wanted it has already put as much as they could afford to risk in.. while the sellers still want to sell and the price is crashing. It's unfortunate that there is so much panic buying in crypto.. because it always leads to crashes.
It's going to be continuing down for a week or two, then I'll pick some up as planned. It's still got good long term potential. Not as much as Nxt but it's always a great idea to diversify.
Also, keep in mind that the reason for the spike was largely because people thought Overstock might go with BTSX.. which is clearly not happening anymore. Also the other big thing BTSX had going for it was BitUSD.. but clearly NuBits is maintaining a much more stable price, while BitUSD has been a little bit weak.