What is the ruling on the rapid heart palpitations, shortness of breath, whispers of showing off (riyaa'), and inability to improve one's voice that affect an Imam, what are the conditions for leading prayer (imamah), and how can an Imam avoid riyaa' and its whispers?

This exaggerated fear of leading people in prayer is not healthy, and you must strive against your soul to get rid of it. If you pray in congregation, then step forward to lead with confidence in God. As for the fear of showing off, that is good, but it should be a motive for sincerity, not an impediment to obedience. To learn about the conditions for imamate, please refer to Fatwa no. 80456.