The speed on these is a little slow.
They don't read quite as action packed as they could, especially if he's freakin out.
I didn't edit the sweat, just the overall motions.

For the trembling you can use an old animation trick called a Stagger.





Here's how it works.
Animate something in a linear fashion.
Moving from start to end.
The spacing does not need to be even, feel free to weight it at the ends or wherever you feel necessary.
(Altho to start try with just even spacing to understand the process)



Then take the frames and shoot them in a "Staggered" order.
The classic format for understanding a stagger goes like this.

Original Frames:     1 2 3 4 5 6 7 8 9 10 11 12
Staggered Frames: 1 3 2 4 3 5 4 6 5 7 6 8 7 9 8 10 9 11 10 12 11 12

Really its just a frame pattern formula.
+2 -1 +2 -1 +2 -1 +2 -1 etc........
This makes the animation move in a given direction but with "resistance".
Try modifying the formula as it progresses.

For this animation my frame order was a little different than the above example, since it ping pongs, and repeats at either end, and i messed with it some.

Original Frames:     1 2 3 4 5 5 4 3 2 1
Staggered Frames: 1 3 2 4 3  4 5 4 5 4 5 4  3 4 2 3 1  2 1 2 1 2 1 2
Staggered Meaning: transition to right  hold and shake on right  transition to left  hold and shake on left

In summary, these 2 animations have the EXACT SAME UNIQUE FRAMES.

Only the order and number of repeats is different.

You'll see this trick used all over the place in old cartoons, like Ren & Stimpy, Looney Tunes and etc.
And video games, SNK, Capcom etc.
It is best used to represent tension, fear, strength, madness, struggle, and such things.
But is a valuable trick for representing many other things creatively as well.

For the gun fire:
Adding a single frame of resolve to the gun when it comes down will help dissipate the fast motion.
Also it could withstand even more speed than I've added here.





I really like what you have!
You're doing a great job!