I think Freemare and Muppetgirl might be right about your horse not firing on all cylinders.
I'm not sure what to suggest...can you get by without tying him too much? Could you teach him to ground tie and do that in some situations instead of tying, or keep him in box stalls/pens/enclosed areas?
It's a pretty crappy situation, but your safety has to come first, and he doesn't sound safe when he's tied.
I guess the only other suggestion is to talk to a vet and see if they can figure something out.