horse stops and shakes like a wet dog while being ridden

Question
My horse was broke to ride a year and a half ago. She was 12 1/2 yrs old then.When I ride her,she stops and shakes like a dog shakes after a bath.She shakes for a few seconds,then starts walking again.She almost shakes me off of her.Is she trying to shake me off?How can I stop this behavior?She's 16hh,1200 lbs.It almost gives me whiplash and rattles my brain when she shakes.On a 3 hour trail ride,she'll stop and shake at least 6 times.

Answer
Hello,
I would check your saddle fit and make sure she is comfortable. She could me uncomfortable with the saddle, her own sweat, or she could be tickled by something. Start noticing if it happens more with a certain saddle or more when she has worked up a sweat. How is she when you curry her? Is her skin tender? When you touch her does she twitch? Once you have ruled out that it is physical you can start to find ways to make the wrong thing difficult and the right thing easy, like making her start working right when she shakes. If you do the same thing every time she shakes, make her work, soon she will put it together that its easier not to shake. Just make sure to check on all the other options first.
Best Wishes,
Caitlin Day Huntress