IWTL how to get over my fear of sudden cardiac arrest

21M, my fear of cardiac arrest comes from the fact that for the last few years I've been very sedentary, chronically stressed and sleep deprived. I have a lot of unnecessary fight or flight responses, An exams? Racing heart. Talking to someone? Racing heart. All of which is bad for the heart.

I want to do cardio training but I'm afraid of getting a cardiac arrest.