I was cantering during lessons just fine last year. I wasn't an expert by any means, but I could go round and round and control the horse, stop him, start from a trot or walk or full stand-still, transition down from a canter to a trot reasonably well...
Then I bought a 12 yo fully broke horse in January (who hadn't been cantered much over the past 3 years) and haven't cantered on her or any other horse for that matter until today. Mostly because my instructor wanted her to get used to our lessons and me used to her.
She has been cantered by an experienced rider every weekend just to keep her in shape, and she does pretty well with her. Sometimes she picks up the wrong lead, but not often. Sometimes she has speed issues, but the experienced rider handles it with ease.
When I cantered today for the first time on her? Yikes. What a disaster. It was so demoralizing.
My poor horse. I bounced all over her back and felt like I was going to fall off the entire time. Her canter is WAY bouncier than the other horse I used to ride, but mostly it was just me. I couldn't feel the rhythm and the worse I was the faster she went. She's very sensitive to leg pressure and I was used to holding onto the other horse or just finding balance with my knees. I can't do that with her, apparently.
By the 6th time around the small riding ring I had improved, but man ... it was not fun for either of us. She was fussy and I was scared and sad that I had lost so much of my skill and balance.
I sure hope this gets better soon. I'm afraid I'm going to start worrying before every lesson and it will make them not fun.
Waaaahhh! I'm such a whiner. :)