Lyman:
Can we agree that loss of SA may have at least potentially involved spatial disorientation?
Maybe. It depends on what you mean by spatial disorientation.
You can have spatial disorientation without any "feel induced" disorientation playing a part, a common affliction in a non-motion simulators. It isn't hard to wind up massively spatially disoriented (where you are in the air and what you are doing versus where you think you are in the air and what you are doing) by having a lousy instrument scan and a bit of a ham fist. I offer myself and my first few instrument navigation sims during flight training as Exhibit A. I think the term "utterly fargin' lost" (or words to that effect) crossed my sim instructors lips at least once. Weak/poor instrument scan and possibly rough hands look to have been part of this crew's problem.
Back to your question.
I suggest that between time zero and time five seconds of this event (pitot data deemed bad and all three rejected by aircraft systems) SA itself was partial to begin with.
Spatial disorientation loss, or at least impairment, need not have been in the "feel" domain at all. Over the past years on this topic, it has been my estimation that an initial "scan impairment" was exacerbated by the mental effort being expended upon "what's it doing now," which takes you back to some fundamental systems knowldege and training issues, CRM and systems trouble shooting methods. Won't repeat them here.
Based on what can be put together after the fact by looking at the record of outcomes (pilot actions with controls and aircraft performance), the degree of SA retained remained at best partial
-- one cue being as you mentioned, rate of descent and the attendant cue of decreasing numbers on the altimeter seem not to have registered --
and I'll even assert that SA decreased as the time moved forward from zero to impact.
In shorter terms, the crew started behind the aircraft, and got further behind as the event progressed.
This in turn leads me back to both upset and "out of control flight." Out of control flight is more or less the situation in which you make certain inputs to the controls, expecting response A, but you get response B (or perhaps no response at all).
You don't have to be stalled to be out of control.
In one fixed wing aircraft I am familiar with, you can be in a spiral (high roll rate/rotation descent) with symptoms similar to but not the same as a spin (which begins in a stall and gyrates as the plane falls).
If you make control input A, anti-spin control inputs, what you won't get is a recovery from a spin (nor the actual spiral) since you aren't stalled in the first place. What you'll get is response B which is that the plane stays in the spiral until you either hit the ground or you figure out what is actually happening and put in control input B, which would be recovery from a spiral and then fly away.
Until you recoginze what the plane is doing (Situational Awareness at its most basic) your inputs may not yield the outcome you expect, nor the one you desire.
Because the flying pilot believed that the plane was still flying (SW noise and other inputs notwithstanding), he made contol input A, kept making control input A even after a few responses to his crew mate on him going up, and he kept getting response B.
The "aha moment" of "we are stalled" never arrived.
SA was never achieved in any meaningful way beyong the pilot not flying
-- observing that the protections had been lost
-- offering corrections to PF in re "stop going up" that are taken form the CVR.
Because this was a crew, I have to assess the SA of the CREW, as well as individual SA of each pilot who made up the crew.
The sum of their SA was most certainly NOT greater than the two parts.
The outputs don't suggest either got vertigo, but "disorientation" in terms not "seeing" what their primary flight instruments were showing them is a rather obvious post mortem finding.
Respectfully asserted to those involved in the discussion at this point:
IMO, somatogravatic illusion is a red herring in this particular case.