I rewatched the trailer again, and replayed a bunch of the scenes over and over to try and look for any pieces to make anymore sense of what is happening.
Right off the bat, during the car crash both the "snake" character and the other individual are in same clothes they are in throughout the trailer. Also, look at what is flying around...shit loads of pills
UK Flag on the wall, I am guessing this would imply location, but the doctors accent is not any accent that would match the location.
"snake" wakes up and while looking at his prosthetic you can see a few flower petals floating around too. Similar to those in MGS3
Throughout the first part of the trailer there is a lot smoke in the air, but I don't think it is smoke, I think it is fog. I'm guessing the "snake" character is still hazy and unsure what is going on.
When "Snake" and the other guy are going down the hall they see what looks to me like a small child waiting by the elevator.
The sound effects are very distorted as well throughout the first half or so of the trailer, gun shots sound off and their is a lot of just odd sounds.
There is that one soldier who is on fire, the second time you see him he looks like he has long hair, almost like Liquid.
Obviously the unicorn and the whale.
I would take a guess that it is one snake or another, but I don't recall any of them ever losing an arm or being showcased with a missing arm. Then again the trailer does not seem grounded in reality. Judging from the end shot of Snake he looks like the Snake from Ground Zeroes, which could indicate it V may be a sequel to it, but who knows really.
The NeoGAF link has a much better analysis than I could ever propose.
Maybe this is all PTSD stuff for Naked Snake?