You and I seem to think along similar lines.

I have also in the past taken a lot of interest in the balance between acetylcholine and serotonin in relation to sleep and waking states. I think it's interesting to note that psychedelics (particularly tryptamines) also increase acetylcholine level and decrease serotonin levels, and I've always thought that this may be an important part of why those compounds can be so visionary and dream-like as well, even though they can also be paradoxically quite stimulating, probably through directly activating only certain serotonin receptors in certain ways as well. I would note though that breakthrough psychedelics can actually make me feel like I could fall asleep as well in the right setting, they definitely have that hypnagogic feel....
With respect to dissociatives (rather than 5HT psychedelics as you're speaking of), I believe that if the theory regarding associations with patterns of sleep regulation is true then I'd speculate that the relevant effects on serotonin and acetylcholine are caused in a more indirect manner than they are by psychedelics. I refer to the following theory, posted earlier:
wiki said:
Another major theory is that the neural bodies that regulate sleep are out of balance in such a way that allows for the different sleep states to overlap [7]. In this case the cholinergic sleep on neural populations are hyper activated and the serotonergic sleep off neural populations are under activated [7]. As a result the cells capable of sending the signals that would allow for complete arousal from the sleep state, the serotonergic neural populations, have difficulty in overcoming the signals sent by the cells that keep the brain in the sleep state
The indirect way I think dissociatives may cause these effects is by simulating natural sleep paralysis by blocking signals from the body to the brain. That is, it is the anesthetic effects of dissociatives that mediate the subjectively dream-like "holing" effects (which may be why the more anesthetic dissociatives like ketamine and MXE are more likely to cause dissociative holing effects). The lack of signal input from the body may be mistaken for REM atonia, which could in turn initiate mental processes affiliated with dreaming. Interestingly, one of the main effects of sleep paralysis is a sensation of movement, which is covered on the sleep paralysis wiki page (such paralysis is very closely related to REM atonia, as it's basically part of the same phenomenon while awake):
There are three main types of these hallucinations that can be linked to pathologic neurophysiology.[9] These include the belief that there is an intruder in the room, the incubus, and vestibular motor sensations.
These sensations affiliated with bodily movement and balance are of precisely the kind we experience in dissociative "holes": tumbling, riding waves or "elevators," flying, spinning, stretching, etc. When one bodily input signal is coming through and others are relatively weaker or blocked there is a lack of coherence or balance in the accurate processing of the information. A signal indicating one is laying still in bed might come in with a relatively higher strength from the right side of the body than the left, for instance, which could conceivably be interpreted as a sensation of "rolling" over, right to left, as is a common sensation during dissociative holes (this example is of course oversimplified for illustrative purposes). This incoherence also enables other sense modalities, such as vision, to more strongly influence our sense of movement, with the effect that "flying visuals" can make us feel like we're flying (resulting in "OBEs"). However, like with most things in the body there's probably a huge amount of interdependence between these phenomena, i.e. it's not just flying visuals that make us feel like flying -- the feelings of movement may likewise lead to visuals of moving through internal landscapes.
I watched The Beatles' Magical Mystery Tour for the first time the other day, and there's a part about 18 minutes in (set to the song "Flying", ha) that looks a lot like the kind of visuals we've been talking about in this thread:
Damn that is highly reminiscent of the visuals we're talking about. It's got so many of their qualities -- flying dynamics, luminous, largely monochromatic features, and organic shapes -- nearly everything!
EDIT
Caution: If you experience the sort of sensations and visuals discussed in this thread, resist falling asleep during the experience. It's sort of like nodding off in the hull of a cabin cruiser while your dad fishes. Motion sickness is a real possibility. (I was already up for over 30 hours when this happened.)