It's sustainable due to wasn't able to stabilized at that certain value, that suddenly collapse after panic sellers dumped their holdings. Nobody options to wait for another price increase, that's why price declination continued to occur sophisticatedly.
So you choose to ignore the 1800 bitcoin created per day? That is a fact and a reality.
There is natural downward pressure due to the miners creating new coins.
Aaron
https://www.amsinger.org