I was a singer, too. I can't recall -- have you had any procedures done? I have never experienced the arm and chest pains you describe. It sounds like there's a possibility you're somehow stimulating the vagus nerve with the deep breathing and diaphragmatic pressure. If you've had a procedure done, that would further indicate this effect.
If you haven't had a procedure, then that makes it a bit mysterious, unless the vagus nerve is responding to heartburn irritation as a result of its proximity.
I lost my singing voice in 2008, regained it after nearly a year on Zantac, then my LPR symptoms increased (and tolerance reached for H2 blockers...intolerant of PPIs) and my voice has been gone for over a year now...