Balanced appropriately for him is the key.
It changes with temperature of the days, grass growing in turn out, loss of hair or growing hair with seasons, age of horse, etc etc etc. The horse determines the balance, not humans or feed companies.
We had a horse that did exactly as you described my company horse instead of a company car. We were not allowed to have our own horses so I sold my tb to have him.
When Mum lost her horse, I bought back James and gave him to her, the quietest tb in the world.
Mum did the right things, she had him on hay only and rode him an hour a day.
It was a week before she called me for help. She took him off property down the road to an oval. She had to dismount. She thought I have not gotten off a horse for 50 years and she remounted. She had to dismount again. She now had a 16.2hh Tb whirling around her to try and walk up a hill along the road to get home.
I was called. I got on him to take him out. He had started leaping. Okay where there is space, Not so okay when he did it in front of a road sign where he was going to land in front of it! Was he going to bounce left or right? Phew I stayed with him.
I took him on a long ride and he settled back to normal.
Yes he was on hay only and being ridden an hour a day but as a company horse I had been riding him 4 - 5 hours a day so that was way out of whack.
It takes them as long to get out of it as it takes them to get into it. It had just happened with James so he came back to normal with that ride I took him on.
With horses that it happens more slowly because of gradual overfeeding it can take them a week or two to get into it, it then takes them a week or two to get out of it.
I mentioned this in my first post when I said I would give the horse a pass as not being too dangerous to ride if it is because of being in the realm of overfed and underworked, which as I said has nothing to do with training.
James was trained in dressage and jumping as well as a trail ride guide.