Seriously it is a different sort of stress, on both horse and rider. To me it is not actually that stressful, I was really happy last week in an indoor arena, with a reasonable audience (who you dismiss from your mind...totally irrelevant to the day) and a judge, who is going to list every way you suck, and also say a few nice things about you.
I like it, I am a dressage rider, which means only me and my horse in the ring, so no worries about anyone else, jut me and my horse. There could be, and are disruptions, and ones that you never think about......Gibbs last year had a small melt down over someone sitting in a part of the stands not usually used.....not any closer to him, just different place, took me by surprise, just didn't expect something to phase him. But over all it is a relatively safe and controlled environment, and I enjoy it.
And, there is of course, as I said, always vodka......
Or tequila, corona, or wine....
I agree with Golden, when I come down center line I don't notice the crowd or even the judge. I'm listening to the reader, I am looking at the letters, I am thinking where my marks are to make a perfect circle, where to make my transitions.
Just like I don't notice the deer, the pheasant, the grouse slamming into my horses chest on a trail ride, the ATV, Or dirt bike, or coyote. Nerves are unnerving wether coming down centerline, coming out of the chute, or going down the trail.
In all it should just be you and your horse doing y'all's best.