I have to say, that is REALLY strange especially from a seasoned lady. Okay, this is my total disclaimer that I am not a vet nor try/want to be one. But here is my two cents!
I have seen something similar, but not the same, in three instances.
One - horse had back problems. Acted like a total freak, lots of tossing of the head and being agitated. Just random acts that made you think he was an idiot. Later found his back was totally screwed up from a spring/summer full of intense jumping couples with constantly swatting at flies. He was in pain and angry
Two - horse was acting really weird when off of bute. Was on bute for a week and acted really out of character when he came off of it - like he was 'withdrawling.' Big burly WB, so theres no way we overdosed him. Just acting cranky, tossing head, pawing, and got over it in about two days. I guess its possible they're like us - you go on 800mg ibuprofen, a bit of pain killers for an injury, and the few days you come off it you are a little *irritated*
Three - Insects. Most horses get used to the constant swatting but a couple get really angry about it. Bees make some horses really mad, ESPECIALLY MARES IN HEAT. Is it that time of the year? :)
Are you sure she isn't reacting to any of the other horses? Maybe there is another mare around her that is making her mad? That would be very possible, since head tossing is an act of 'defiance' sometimes. I hope this helps. I am not going to try to connect dots, I just thought you could take or leave this and see if any of these horse behaviors I have seen seem to fit your situation, and go from there. I hope your mare gets to feeling better !
Last edited by 94broncoxlt; 04-04-2012 at 01:06 AM.