Realize that happiness is not something that is determined by outside conditions, but rather, from internal considerations of personal responsibility and authenticity. If you don't get into grad school, life will continue as before, but on a different lifetrack. This is no different than the rest of your life, which as I am sure, has not been completely predictable. Go with the flow, enjoy some chemicals, and recognize that academia isn't going anywhere.
p.s. Unless you are a zen monk, you will probably always be anxious in these situations, but anxiety is a normal human emotion, so it is no big deal and it will soon pass.