I don't know the entire story on your horse......but there is the possibility that the previous owner drugged the horse to get it sold. It's actually kinda common to find some people in the horse trade who are interested in nothing more than money.
But before you go throwing your own money in every which direction....lets see those hooves. There's some pretty good hoof professionals that frequent this site. Google, "taking good hoof photos", for some direction on how to get good pictures that will allow us to see any possible distortions of the hoof.
The hoof is the foundation, and any imbalance in that small portion of the horse will translate to large disturbances in other parts of the horse. It really could be as simple as the horse needing some good trimmings to be brought back into feeling good. But it also may be something else. Though I suggest you start there first.
Truth passes through three stages. First it is ridiculed. Second it is violently opposed. Third it is accepted as self evident.