Unless you are doing day trading or scalping, the best thing to do is, of course, just HODL to what you've got and patiently wait for some days because we all know that the market will eventually make some rebound. The surge back may not be very dramatic and can be painfully slow but definitely there is no question the market will be coming back (and it is starting to move now as I am writing this reply). This big dip is traditionally a part of the market history and this should not be surprising anymore though admittedly it can be a little bit painful. The big lesson here is that we should look at things long-term rather than be focusing on the day-to-day market movement. We should have that vision of what we want and we should get educated with the things related to cryptocurrency.