Nerves.
This is natural and can be lived with and yes, it is an adreanal surge of hormones preparing you for fight or flight. The surge of hormones also cuts off the digestive system and prepares for shock.
The only way to overcome this is with exposure to events that trigger it.
Learn to love the surge of hormones and know when it happens you are about to do something life changing.

I have been in so many fist fights and I also hunt and know the feelings you describe well.
If I am looking to commit to a punch up I shake like a rabid dog until I harness the adren and go for it. that surge then carrys me through.

I also get this on a hunt as I sight the x-hairs on the prey. But in this circumstance I must control the surge as it is not required and can spoil the shot. If your killing an animal in a humane way then the last thing you want is the shakes.
It is a matter of dissassociation (I know I cant spell)and a form of meditation to reduce the effects of the surge and focus on the task at hand.

It is a matter of embrace or ignore, being if you need the surge or if you do not.