So I have noticed this problem lately, whenever I am playing in the mid-high register I notice my jaw getting super tense and if I play like that a lot I'm tired after like a half hour. I honestly for the life of me don't know how to fix this. I do breathing exercises and all that. I don't play perfectly centered, I actually use a little more lower lip than upper, but I think it's because I have I have a slight overbite and more air can get through if I tilt my head or the horn. But does anyone have any tips of how to fix this? My neck tenses up too. How do I open my throat? Should my neck look the exact same as when I'm not playing or blowing air?