De-Stressing/Staying "Cool" At the Office

Hey ladies. I'm a bit of an emotional/over reactive person, and I don't like it. I try to be aware of it when it's happening, but I don't know what else to do. Work has become stressful over the past few weeks (big project release coming up) and last minute issues are popping up left and right because people let things slip through the cracks. I of course get disproportionately frustrated and it takes a while for me to calm down. Note: I do not yell at people, but I hold onto the feeling of frustration and I feel it affecting my mannerisms, by expressions, body language, etc.

I want to be less reactive/calm down/keep my cool at the office (and life!) and need some advice. Any ideas??? Thank you :)