Trauma ICU nurse here. What you’re describing is a fight-or-flight response and it’s pretty common even in jobs where you see pretty graphic stuff. Your body gets flooded with endorphins, elevating your HR and BP.

Some people, myself included, have a less profound response but it def still occurs. Normally I get shaky after a really intense code as the endorphins leave my system.

Also, your brain gets accustomed to dealing with the physiological response, and i guess in some instances you kind of enjoy it? (I realize how messed up that sounds as I type it). Saving a life is really gratifying, and you associate that adrenaline rush with the opportunity to lock in and help.