Ridergirl, a dominant horse does not actually WANT to be the boss. Being the boss means they have to call all the shots, and when put in a confronting situation, the dominant horse has to take charge of the situation. Most horses tend to be far happier in themselves when they know where they stand. And I don't think Chinga is entirely sure where he stands. Yes he's a dominant aggressive type of horse, but I think it's very much a show, that is to hide the confusion he is feeling. Horses will react in one of two ways, fight or flight. And Chinga appears to react to pressure and confusion with 'fight'.
He definitely needs to be dominated and shown that people are not going to put him in a situation where he will be hurt. He does not have this at the moment, as Maddie is just not assertive enough to show him this, so he feels as though he needs to be the dominant one, because no one else is.
This horse isn't 'suffering' per say, but to allow him to continue on as he is would be very destructive to his mind and he certainly has the ability to turn into 'suffering' horse.
Maddie, I'm glad you're sending him to a trainer for 90 days and are getting involved in the process. I was under the impression that it was only going to be a short stint at the trainers like last time. If the trainer is willing to work with you to help overcome your own fears, it may well be the break that Chinga needs. But you HAVE to always keep in mind that just because he does well at the trainers and comes back all lovely, does not mean he won't turn on you again. He seems to be the type of horse that is always going to be pushing, and if you don't keep on top of that and nip it in the bud each and every time he tries it on with you, you will end up with him right back at the start and the money at the trainers will have been wasted.