why the price has fallen so much, now one coin costs 90 satoshi ?? !! ...
It is because DIG is a crypto asset and this type of assets has a strong tendency to fall and rise dramatically so in other words you can gain a lot of money BUT also you can lose your heap of cash if your prediction of price moving was incorrect. So there is no surprise in this particular falling down further more it's not in the first time.
P.S. A little tip: Wise investors buy on bottom.