Here's a good example of what can happen:
Forrest Griffin is the former UFC Light Heavyweight Champion and is well known for being able to take massive punishment. In the following video at 6:28, Griffin is fighting Anderson Silva, who is probably the most accurate striker in MMA history. It looks like Griffin is merely tapped by Silva and he collapses like a rag doll...
Anderson Silva Highlight Compilation (Best MMA Fighter Ever)
Many times, a fighter is caught with a good strike to the head and they are declared technically knocked out. The fighter almost always is still active, grabbing the opponents leg or the ref and they refuse to believe they were TKO'ed until they see the replay on the big screen. Zimmerman would not even know he was briefly unconscious.
Also, other commentators have said that blocking someone's airway is not part of MMA. Such ignorance - it's a BIG part of Brazilian Jujutsu (BJJ) and "ground and pound".
So, combine an initial strike to the head that breaks Zimmerman's nose, with his head hitting the concrete, then having his breathing disrupted - I would be surprised if he wasn't at least briefly unconscious and highly incapacitated from lack of O2 without even knowing it. I've seen it many, many times during MMA fights (one of my favorite sports).
All this, plus Martin having Zimmerman under "full mount" which is almost impossible for experienced fighters to escape under the best of conditions, then Martin goes for Zimmerman's gun... no one could deny that Zimmerman was in serious trouble!
And that's before the state of Florida decided to ruin his life.