Yeah I know exactly what your saying. It`s really hard to make your mind believe what you know is right. Your subconscious fights you all the way. Anxiety is a learned behaviour so it can be helped and eliminated but its something that takes so much time and patience to overcome.
My anxiety has been a blessing in disguise, it really has changed my life for the better. It has made me step back and realise my life before was just too crazy and now i`m starting to train to become a counsellor to help others through the horrible feelings and thoughts.
Your heart is made for the purpose of beating fast when needed eg; running etc. So if you can do that then I think your heart should be up to it. I got scared through my anxiety about my health so I lead a healthier lifestyle which certainly helps my horrible thoughts.
Good luck with everything
debs