Hi. I had a hyperplastic thymus with thymoma. The thymoma was benign. You're asking me to go back 16 years when the surgery was done, but breathing has never a problem for me. I have generalized MG, so muscle weakness and fatigue were my main issues. You're correct, the mass doesn't change by the hour, but things can go bad if the thymoma is neglected. To be honest, I never "felt" the mass and was totally clueless until the results came in. Let me know if there is anything else I can help you with.
Jim