I had a gymkhana this morning, and my gelding and I were doing great on all the events until barrels. He'd made a really nice run so far, and right after the third barrel, I asked him to speed up by clucking to him. He sped up, and was fine for about five strides. All of a sudden, I felt him tense up out of fear, and he did a half-stop, and started bucking. I flew over his shoulder and hit the dirt, hurting my ankle and shoulder. He bolted, running around the arena madly. He' NEVER tried to buck before. A lady caught him for me, so I got back on him and re-did the pattern at a trot. He was perfectly relaxed, and was well behaved. Even though I rode him after I fell off, I took a big blow to my confidence. Any advice?