I always seem to get that boost in adrenaline and have to calm myself down for the shot. Start breathing heavy and shake some.
Last yr I had a strange experiance with a doe. I saw her about 70 yards out and she worked her way up to me. (I was using blackpowder) took maybe 3 or 4 minutes for her get to about 35 yards and gave me a perfect broadside shot. I was as relaxed and calm as if I was shooting targets in the back yard.
I never got the boost in adrenaline or the shakes. But once I fired the gun it kicked in, she ran towards me and stop 5 yards from my stand and fell over dead. I found it weird at first that I was so calm for the entire time.