If your in an enclosed space, make sure your okay and just wait if the situation is dangerous (dangling reins, tippy saddle), he will calm down on his own.
If your in the open, and your okay, go get grain or something he likes like the cookie bin maybe, and see if you can lure him close enough to grab a drink, move quietly and slowly talking to him in your normal calm cheery manner.
Bright Sunshine with a few High Clouds
