It looks like all altcoins dump 10-20%. What is the reason?

I am very sad

Why are you sad? It is the way the market works. I bet you enjoyed the various price surge? It is time to take a hit. Dry your eyes man and suck it cup. It cant always be profits.
Yes bro. It cant be happen not just one so be open minded dont be sad be possitively to face trading world. Up and down system try to think that its just a test on how you can stay for it
if you can survive this one for sure a lots of things that will happen to your trading activity will be a normal thing for you, most of if seems to be on its downfall and fortunately we cant do nothing what we need to do by now is just to observed and make sure that we are not doing a panic to avoid big loses.