I managed to get another lesson today and I definitely noticed that things didn't feel quite right when I was on the wrong diagonal. I also worked on my canter (my back aches like mad after that and yesterday!) and I noticed that when I was coming back into rising trot, I always seemed to come in on the wrong diagonal. But I know I need to work on my timing for that so I don't end up bouncing in the canter or
getting a great big jolt from the trot.
Cantering was really fun! My dad came to watch, and filmed me too - I have loads to work on, of course, and the video definitely picks that up - and I had such a great time! Charlie B will drop back into a trot if you let him get away with it, but I had him cantering all round the arena until I asked for a trot. I felt so much more secure in the saddle, too. Yesterday I had a lesson doing the sitting trot without stirrups, just as upnover recommended, and I learned a lot more about my seat. I also felt the difference between a slow walk and a marching one - moving side to side with his hips, and moving backwards and forwards with his back.
Thanks, everyone, for all your advice and help
I've been remembering it during my lessons and it's helped me a lot. As final proof of my progress: I'm now aware of it when the horse is going to the loo xD