a friend of mine was having the same issues (@ least from what you have included) of her mare being witchy when she never was before. She had her tested for lyme (we live in mass) she was found to have a high test! they treated her w/anti biotics and she was on that for a while. after she was all done w/meds she was still not the same, SO final resort..... get this..... they put her on horse BIRTH CONTROL!!! have you ever heard of such a silly thing, but IT WORKED!!!! she is back to her normal self... goood luck, something to think about. Oh yes I totally agree w/the others on having the vet some out to do stress test, talk to the vet about the birth control thing too and see what they think, couldn't hurt.