I found that breathing exercise really helpful: breathe in (5sec), hold your breath (5sec), breathe out (5sec), wait before you breathe in again (5sec). It can be a bit difficult at the beginning but it really helps!
During the horse show i think about my posture that does that i think less in not knocking down
With that i am calm
Close your mind off and only think about the course and what you need to do to have a good round
I get the same as you and what helps me is to remember that if I'm nervous then my horse can feel it and of you horse messes up (tripping or stumbling when jumping) the it can be a bad result. Do the best for you horse and not for you
Try take some "Rescue" tablets before the show, learn some breathing techniques and also eat food that won't upset your stomach, I've heard Bannanas and apples are a good choice. ☺️
Oils* it auto corrected to pils sorry lol
Check out this company called Oilystable, they have pils for your horse and you. The company is a "section" of Young Livong Essential Oils and is really helpful. I recommend checking them out and reading about the Oils. My friend's parents own the company and you can definitely trust what you get! :)