I'm not a NH person, but I can relate to the feeling, OP.
I had a breakdown while working with my dad's 6 year old mare. She was just ram-jammed into work, getting quick training as she went along. She hardly had any extra time spent on just her training.
So, I put a snaffle in her mouth and went back to the beginning. About 3 weeks in, while working on her loping issues (Running through your hands, lunging into the lope, always breaking gait when asked for a circle of any size, and sort of turning her ribcage out of the circle) I lost it.
I ended up slamming on the brakes and used my leg and split rein not so nicely to get the "move your ribcage in" idea across as well as getting back into a lope, and doing the same then, and then when she tried to ignore my hands, or switch to the wrong lead when she didn't want to circle, I'd pull her into a spiral, also not too nicely.
I also yelled at her, and tried my bestest not to cry (It's my reaction to frustration...). So, I felt super discouraged and went back to the farm, gave her some "I'm sorry" oats, and let her back with the rest of the horses.
But on the upside, it seems that I did actually get my point across in the end. The next time I actually wanted to ride her, she was almost a totally different horse. I'm actually using her for teaching myself English right now.