If you have access to an indoor when there's not an event going on, bring your horse in work him on a long line. He'll probably fly around like a lunatic for the first 15 minutes or so, but once he begins to settle down, start working with him by changing gait and direction often. He needs to know you're there to be a leader and manage the situation. Be very careful to keep you own energy calm. If he's a complete snorting nut job, just keep it at a walk. Once you see signs of relaxing, (lowered head, licking lips, blowing out not like a dragon) reward him with a soothing voice or some pats. Whatever you do, do not let him leave the arena while he's in flight mode, or else you will re-enforce his fear. End it on a calm, good note. I've done this a few times and it works very well. Good luck.
You just have to see your distance...you don't have to like it.