What I do..
I have had my handful of real bad beats such as getting a 4 of a kind out rivered by another 4 of a kind and in moments like this you stand up, take two steps back, let out a big goku like yell then make a pb&j to calm the nerves. Food always makes the body relax and feel safe again so your nerves can calm down to normal and you can play emotionless again.