Just to clarify for some, Sean Murray is NOT sick. People are jumping to conclusions based on his weight loss and his voice. He went on a special diet to drop his weight, and since the vocal cords are muscles like any other, they can change when diet and exercise routines change as well. He's fine.
Thing about being shot, even with kevlar, at point blank range it is still powerful. It could still knock a person unconscious and even cause injury. And as was said, he could've been injected with something to make him appear dead long enough. Kinda like they did with Fornell back in NCIS Season 2 to fool the mob.