I have a horse I work with that's a 20 year old quarter horse that has now done this to me. It has happened after riding and cooling him down and putting him away or getting ready to put him away that he all of a sudden hangs his head low as if wanting to roll, but his eyes are "vacant', then he kicks with his back legs out to the sides, VERY stiffly and almost stumbles. He's very stiffen legged in the front as if bracing himself. It all happens within seconds. Then he lifts his head and appears normal. It definitently looks to me to be something neurological. Has anyone else had this happen to them?