Hi:  I have a lovely 4 yr old mare that I've owned since Christmas. She has a nice temperament, responded incredibly well to join up sessions, and is going nicely under saddle but very green. She was only backed in November 2020.  She is not an overly nervous horse, but the type who reacts immediately to a perceived danger and then quickly relaxes when she realises everything is okay.    About 2-3 weeks ago while riding her in my arena, she did a full body shake with me in the saddle - very full on and difficult to sit. It frightened her because I obviously moved in the saddle with the shaking and she jumped forward. I managed to stop her and then we kept on at a walk. I tried not to make a big deal out of it, and just keep walking.    Today while my riding instructor was here, we had been having a lesson for about 30 minutes and it was going well.  She again did a full body shake and really dislodged me - this again frightened her and she went into real bucking - front end came up, and I went up into the air. Back end came up, and threw me forward. I just about gained my seat, but then the front came up again followed by the back and I actually fell off over her rump, landing hard on my shoulder and wrenching my ankle which was initially caught in the stirrup. It's the first time, in a life time of riding, I've come off over the back end. She never tried to kick me and was clearly frightened as she ran to the end of the arena, head up and full of tension. She calmed down almost immediately as my instructor is very quiet with horses and went over to her after she made sure I was okay. It took me awhile to get up as the shoulder and ankle took a real beating.   This problem seems clearly a fright/flight issue and I don't want this to become something habitual. She shakes, she becomes frightened, she bolts or bucks.   Does anyone have any suggestions how to reassure her if she does feel the need to shake (it's very hot here in Australia now so she is sweating a bit when being ridden even for a short period of time). I thought about long reining her with the saddle on and hoping she might do a shake with the saddle on a few times and realise it's not something horrible on her back about to eat her. Problem is, with a rider on it's a whole new issue as it's very hard to stay stable and not move when a horse elects to have a really thorough body shake.   Thanks for any assistance that can be offered!