My mare has suddenly gone from not wanting to slow down to not wanting to walk. She is fine on the ground, will walk and trot in hand no problem. She now suddenly stands still for mounting, and not even a cowboy kick gets her moving. Once she is moving and gets excited, she will get quick. I don't believe this is a lameness issue, as she does not miss step or appear to be limping and a walk trot or canter. Do You think I have found a loophole in her training from somewhere in the past? I have been working with her for a year now, and this is the first time she has done this. Opinions?