Not sure if this should be here or under training... putting it here for now, though. Also, there may be a thread on this already.... sorry. Suddenly (and I mean suddenly, as in this has developed over roughly five days), my six-year-old QH mare, Meeka, has become rather aggressive. Can anyone think of a possible reason why something like this could happen? This mare has always been a sweetie - up until two (maybe three) months ago, I've never noticed when she's been in season. We see her every day, for hours at a time (normally - if the weather is bad or we had classes, sometimes it'd be for less). I can count the number of days that we haven't seen her at all on one hand. We've (my sister and I) owned her for a little over 2 1/2 years. She's always been a little girthy - since we purchased her. We've had the occasional mood problem, but very few and very far between. This past Saturday, a mare at the barn where we board was put down. I think that's when all of this started. I got up to the barn late (due to work), but my sister and cousin were there early. Meeka was going nuts (side note - anyone feel that when a horse dies, all the other ones sense it?). My sister apparently tried to ride her but she nearly bucked her off. She was loose in the arena when I got there. I was finally able to catch her, but she was going nuts. All the horses were acting up, so we initially brushed it off as such. She was no better on Sunday, trying to bite us and, at one point, even turning her butt at us - something she's never done before. We saddled and rode her on Monday and she seemed alright. Kind of skittish with the reins, but overall better. Last night she was back to being aggressive, and tonight was no different. She was like this even in her stall - we'd try to touch her, she'd pin her ears, shake her head, and bite. We did ride, for a little - she was fine then (we rode bareback). When we put her back in her stall, it was right back to the ear pinning, biting, and such. She's hasn't been ridden as much as normal due to cold weather - as far as I'm aware, she's been going out Monday through Friday as far as turnout goes. She gets two flakes of hay and two cans of grain daily - same diet since we got her. My sister and I have it narrowed down to three things; pain, being in season, or possibly her just trying to be the lead mare. In the group of horses that she's with most (which would be my other mare, my friend's mare, and my other friend's mare and gelding, although she doesn't see the gelding a whole lot... also occasionally another boarder's gelding, and his extremely alpha mare), she is alpha. Not sure where she is in the turnout field - there's roughly seventy horses. I would venture to say she's pretty high up, IMO. Saddle fit is fine. She's ridden in a D-ring snaffle. She was never particularly mareish ever (which I know I said before), until we got Lexie. It seems that Meeka's picked up on that with her, and is becoming that way, too. She's eating and drinking as normal, and also going to the bathroom as normal, too. Two other hacks have come back to the stable, as well. I think that's all that's been going on of late. I honestly feel like I hit a small roadblock here. I would like to give her Mare Magic (as I do for Lexie, and it helps her A LOT), but it seems like she may be allergic to it, as she coughs when she eats it. I've thought about calling the vet, the chiropractor, starting her on a different supplement, possibly even calling a trainer.... it did cross my mind that she's just messing with us, and trying to become our alpha, so I've been trying very hard not to get scared and act tough (easier said than done). I don't know.... this is just so weird for her. It also seems like since we got Lexie, Meeka feels stiffed and her bond with us is fading.... which was never the intent. Like I said, she has never been this aggressive, though. Could something like this be mental, as well? My sister and I are thinking of just starting to rule things out.... what would you guys do? Any advice is appreciated.