Zero doesn't care for the other patients - they do not have muscular bodies so they're not soldiers and therefore they are probably just normal patients - and orders a shoot-to-kill operation to retrieve BB. Then, Zero, who's purpose of sending BB to a Cipher hospital was to keep him in-check since it is well-known that Zero likes to keep BB under his control in one way or another, orders his Cipher troops to invade the hospital to capture BB - since he now no longer has any severe medical issues (after all, if BB is in a coma, they can't just keep him locked up in a cell, they have to wait for him to awaken to be sure he's okay). This woman is likely a nurse letting Cipher (Zero) know that BB has awoken from his coma OR she is an undercover DD operative, informing DD that BB is awake, and to put into motion DD's rescue operation - either way, DD finds out that BB has awoken, most likely due to the invasion of the hospital that ensues, which they were anticipating. This would mean 'V has come to his senses', with 'V' being patient number 5 - BB. The end of the trailer has a female voice say 'V has come to'. This could explain why Kaz is missing from the hospital (although he definitely would be discharged much earlier than BB), and why no one BB knows is even there, or anything pointing towards someone he knows ever being there - Diamond Dogs (DD) couldn't enter a Cipher hospital nonchalantly to visit BB. We believe that this hospital is a Cipher hospital under Zero's control. So Big Boss (BB) awakes from his coma, the British flag on the wall indicates that he is in a British colony and also alludes to it being related to Cipher. The following is based off these videos, as well as previous game's lore:

I'd recommend only beginning to read it if you are a die-hard Metal Gear fan and/or are deeply interested in Metal Gear story/lore, since it's pretty damn long. I'm very sorry if I've made any errors but we ran this through our info and timelines to see if it makes sense and it's plausible and checked out fine. Please pick apart any things, and give some feedback. If you're not familiar, watch the two videos below~ Hi! Me and a friend have came up with a solid theory about the first scene of TPP - the hospital scene.

Mgs5 female skulls music intro