For me i would just be calm and be patient because this is normal in cryptocurrency, there will be always ups and down. Best thing to do is hold then wait for the bulls to comeback even if it take years or more.
It is very easy to say that we are going to remain calm under the current circumstances but anyone that invested at the end of the year of 2017 is going to have a lot of problems remaining calm when he has lost more than 80% of his investment in less than a year, I know that those that invested at that moment in time can still get profits if they hold long enough but those people never had the intention of doing something like that so remaining calm is going to be very difficult for them.