I did this when I went to college. The English riding classes were the only ones that fit my schedule, so I took them even though I had never ridden English in my life. I hated it at first, but it was the only way to get to ride. I found the saddle uncomfortable, and some days I'd get so frustrated with it that I'd opt to ride bareback. A dressage saddle isn't as different as a jumping saddle, so those are easier for me to feel balanced in. I've also had a hard time learning to maintain contact. I like to let my reins slip looser, especially at the canter. This was less of a problem at the university, where I was jumping and doing more hunter type stuff on western trained quarter horses, but is making learning dressage really hard. I also had to learn to post the trot, which I still don't like, but appreciate more now that I lack ab muscles. I'm making it sound like I don't like English riding, but really, I do, it has just been harder for me to adapt. I enjoy jumping and dressage both, and they give me goals now that I don't have a ranch and cattle to work. Gives me something to do in a small space, too. I also think that English riding requires a lot more rider skill and precision, while the kind of western riding I did (ranch work, working young horses) requires a certain confidence and relaxation that many English riders lack. I never showed western or did much arena work, so maybe that is part of why they seem so different to me. Good luck with your switch!
Tug on anything at all and you'll find it connected to everything else in the universe.~John Muir