I trialed a horse one day to buy him (and didn't!) and he did exactly that, then someone I know bought him and tried all they could to train him up, they also had chiropractors etc out to him after he wouldn't stop doing it. They then found out he had ruined a neck muscle (I was told he snapped it but i'm doubtful on that) he ended up being put down as it couldn't be fixed.
Are you sure she's not in any pain? Danasinga didn't show any signs he just suddenly exploded and left me winded on the ground.
Maybe that saddle doesn't fit right? Even though she showed no signs she still could have been in pain.
(I'm not trying to tell you she IS in pain btw, who am I to know
just suggesting it from my experience)
R.I.P ~ Bubbles - 25yo tb mare - 13.04.2011 ~ 8:30am ~ passed away naturally and peacefully in my arms