From the way it's drooping more in "back" (wall side) than in "front" (door side, I'd say one of the wall fasteners has been compromised.
I've had both of mine down (made new ones just on style preference) so I can tell you how mine were attached by Chinook.
First of all, the attachments are basically made in two places:
1) A rail that runs along the top of the cabinet, just inside the doors (up by the built in lights). Screws go through this rail (clearance holes) and then into the lower fiberglass roof skin, and after that the roof core (plywood in those areas on my rig).
2) A rail that runs along the bottom of the cabinet in the lower corner where it meets the outside wall (i.e. just above the valance lights). Screws in this area go through the rail (clearance holes) and then into the side wall of the rig - through the 1/8" fabric covered wall panel, and then into plywood that is in a huge piece that surrounds the window frames (and is held to the outer skin basically by polyester mush, from what I can tell).
On the sink side, I think mine might also have had a couple of screws into the plywood shower common wall (on the after end). On the dining side it connects to the microwave cabinet, so no real end to attach to there.
It's possible that water can leak in, rot the plywood core, and then the screws let go. That happens on boats (core rot). But even without that, these are HEAVY cabinets, and sort of only held in by screws in tension (upper). Granted the wall screws are more in shear.
I weighed one of my upper cabinets after I removed it and as I remember it was close to 100# (or at least 80#). Those oak doors are heavy, and MDF isn't light either.
I'll see if I can dig up a couple of photos....
Oh, so anyway, presuming there is not some giant scary rot issue, you could potentially move a screw over (add one) with a new clearance hole(s) in the rail(s). I think it would be possible for one to fail (break or pull out) even without a rot issue.
BG
PS: Upon reviewing your photos again, I see that it's the driver's side cabinet front end wall side that has drooped. That end is basically hanging out in space (vs. the shower end that has a side wall to attach to), and here is a thought: The large plywood surround for the window DOES end in this area, as of course the shell starts curving. Maybe they missed the end of it (or barely caught it) with the forwardmost screw(s) on the "wall rail" of the cabinet. You could just try to re-affix, but if you want to know more, if you remove the driver's side fiberglass pillar, you can reach in around the wall panel and feel what's going on. [Edited to change something: Actually, the area you want to check is adjacent to the fiberglass entertainment module, not really the vertical pillar. So you may be able to reach around inside the entertainment area, and/or see what's going on by lifting the false floor of the cabinet itself. I had both the entertainment and pillar fiberglass modules out, so I had free access.] I wouldn't think that would be the most likely area for leaks, since it's not below a window or on the roof, so a leak caused problem wouldn't be my first suspicion.
Okay, back with photos. So first of all, here is a wall drawing. This is the passenger side wall, but you get the idea. The diagonal lines around the window represent two 1/2" thick pieces of plywood back-to-back, for 1" total. In this case the upper wall edge where yours has come adrift would be on the left (but opposite since it's the driver's side). You can see how the end of the cabinet fasteners could potentially miss the end of the plywood (if that's what indeed happened, of course we don't know yet).
I had to reduce this, so you'll likely have to click to make it out.
And here is a photo of one of my removed upper cabinets. In fact this is the driver's side cabinet, at the forward end, right where yours has come adrift. In the lower left of the photo, you can see a round hole with a wire coming out of it. That's the corner/edge where it looks like yours has come off. You can see a little "cleat" along the lower (in photo) edge: That's the lower cleat that runs the length and has screws through it going into the wall - it holds the back of the cabinet to the wall. At the upper edge of the photo, you can see a wider cleat (board) that also runs the length. That's where the overhead screws go up. That one's wider, IIRC, because it supports the hinges for the doors (I may be mis-remembering it exactly - anyway that doesn't matter at the moment).
If you go poking in to see what's what, know that you can remove the white carpeted "trim" pieces, and also the floor liner of the cabinets. As I remember it you remove the end ones first, then the skinny strip on the outside wall (under the roof "swoop"), then the oak septum divider in the middle door area, then the "floor."