Horse keeps throwing me off for no reason

So, I’m not having the issue of being thrown by Jenda anymore…but some other weird behavior has popped up. For the 3rd time in 24 (real life) hours, it seems as if I’m getting thrown off when stationary. Like this morning, I was hunting hares in the Rattay woods to fulfill a quest for the peasant Alex. And then, I took a 5 min break, sitting atop the horse in the saddle. WhIle sitting at the keyboard talking to my girlfriend, she says “it looks like your horse just had a seizure”. And so I look at the screen right on time to see him laying on his side on the ground, convulsing like an epileptic. I’m waiting for it to happen again so I can get a screencap. If I walk away I can call him again. But it only seems to be happening when not moving, and fortunately not very often. I have never had an issue with any horse except Jenda, I may go back to Al-Buraq, even despite his slightly lower carry weight.