You are not stress...you are experiencing stress. You are not anxiety...you are experiencing anxiety. You are not fear...you are experiencing fear. You can recognize the fact that you are not your emotions and simply accept the experience of that emotion and move right through it.
Seriously, if you always put limits on what you can do, physical or anything else; it'll spread over into the rest of your life. It'll spread into your work, into your morality, into your entire being... There are NO limits. There are plateus, but you must not stay there, you must go beyond them. If it kills you, it kills you. A man must constantly exceed his level.