During my last sit: Full-body observation, feeling of swirling/whooshing energy throughout torso/head, very harsh, wide, "helicopter blade"-speed strobing vibrations in the center of the body. Painful, harsh vibrations in back of the neck and pressure inside the skull. Observing all of this in some sort of Jhanic state, however the "central observing apparatus" is very much intact, feels as though awareness is somehow stuck to a wall, and everything else is occurring "in front" of that.
Late 3rd jhana, most likely Re-Observation.
General feeling of "make it all stop" prevailing, yet am unable to see through the centerpoint, cannot perceive formations yet.
9th ñana, Desire for Deliverance.
How do I go about shifting perspective to penetrate the central observer/"self"?
This isn't easy to do while in Dark Night as the focus of attention is very much pushed out to the sides, the center point is difficult to see and to force it is to make a mistake which can be easily avoided. Rather than trying to fight with it, learn to make use of the natural focus and pay attention to what's happening 'out there' because trying to force the focus to be anything other than it is at this point will cause unnecessary suffering.
In other words, it still feels very two-dimensional, even though sensations within the body are being followed with ease and precision.
That's fine, just continue to note accurately and it will open up naturally as you move into 4th jhana.
My guess is early Dark Night or falling back to Re-Observation?
I'd say it's probable that you're getting into Re-Observation, possibly getting a whiff of Equanimity but not quite.
There are times of very accepting, patient Equinimity, which sort of accepts and tolerates the harsh vibratory stuff, yet it does not feel like Iike I am making any progress toward a Fruition. Strong knowledge of misery/fear/disgust, strong desire for Deliverance, but a prevailIng "stuckness".
It's worth remember that one of the factors of the 3rd jhana is equanimity, if you can tune into that then you're doing well and it's worth making use of that when the harsh vibrations of 10th ñana appear, observe them with equanimity and see them as being no more or less important than any other pattern of sensation you've experience so far.
Note those sensations of "stuckness", what is it that's "stuck"?
You say that "it does not feel like I am making any progress towards a Fruition" - What do you think would indicate that you were making progress?
Where to direct attention?
Work quickly and precisely and observe how every sensation is subject to the Three Characteristics. The endings of sensations will be more prominent at this stage, pay attention to this and see how every single sensation, even the pattern which create the impression of there being an observer, passes away in the same mechanical, predictable fashion.
By the sounds of things you're doing fine so far, but I don't think that you've gotten stream entry yet, based on what you've said so far at least, so your priority should be to get the momentum up for landing 1st path. If you improve your practice and just stay at the sensate level observing the 3C's then you will absolutely get this done, and I don't think you're a kick in the arse away from it if you're not already there. Either way, the 3C's is the way to go.
Your descriptions are fine, don't worry about it.
Best of luck.