Selling should not be your first response to a dump or bump rather, you should look at more factors that constitute the situation of the market and the quality and future success of your holding should be given priority!
And in a situation where things seems like its really not going to work out, the best thing to do at that time is to sell what you have and hold the little profit you have been able to make, instead of losing every thing just like some people did now.
Some people keep on believing in Hodl and end up losing everything, which is not good. They keep believing that the best thing for them to do is keep on Hodling no matter what. But I dont believe that, its best to take your chances.