Sometimes when I get overwhelmed I have to take a couple seconds to stim and breathe and then I can start to focus again.

hello, fellow musician! I myself relate very heavily to this. when I’m in my choir I tend to get lost within sheet music because I will simply be listening to the music and humming the notes rather than following the words and actually making an effort to read. personally what I do is I attempt to separate each feeling I’m having and I put them into categories in my head. thinking of it like you’re putting that thought/feeling/distraction in a box. then, identify the task at hand that needs to be completed most urgently out of every other box. then, mentally, you can move those boxes aside and just focus on the one task, which for you in this example, is the music. you can also make practice like a game. what I would do with music is make small notes of my favorite parts, whether it be a few notes or a few measures, and I think of the song like a story, and the favorite parts of the music are like introducing a new character/event/conflict. change it up every time you play it if you want! this gives your brain an objective while going through the piece. when you reach a certain point, think this, when you get to another point, think that. make associations of outside things with parts of the music so your brain can actively identify it while going through the piece. I hope that makes sense, I tried to explain it from my perspective of music. let me know your feedback and if anything helps!