Much like how the psychedelic experience can be explored through the use of psychedelic substances, dissociative hallucinogens exhibit a similar system of intensity. One of the main differences, however, is that mild effects do not just increase with dose, as psychedelic effects often do. Depending on the dose of dissociative, a whole new "plateau", each with it's own list of effects, benefits, and downsides, is reached. Their are four such plateaus, with a hypothetical fifth. They range from stimulation (which is oxymoronic when speaking in terms of the dissociative anesthetics) to severe dissociation of mind from the body, often times an experience that is not wished to be repeated.
With dissociatives, the plateaus are very much depedent on weight and metabolism, as well as a variety of other minor factors including how recently one ate and how much one ate, etc.
It is often said that the first plateau is the hardest to achieve; you have to gauge your dose carefully in order to reach it. Generally, this is a threshold experience; slight stimulation, euphoria linked to music and motion, very slight intoxication (similar to alcohol but the mind is less "cluttered"), etc.
Usually, after tolerance builds, this plateau can't be reached again because of the sheer fact that it is so subtle. The most pronounced effect upon a first-plateau trip is the alteration of music appreciation. Many people report musical euphoria at this plateau which is synchronized with their motion.
The second plateau is almost identical to the first but with more pronounced effects and a few additional ones as well. This plateau is when an overall "stoned" feeling becomes undoubtedly apparent within the user. Sight and sound begin to take on dream-like characteristics. Motion euphoria slightly subsides, while musical euphoria is slightly increased. There may be small bursts of sensory deprivation; periods where repeating surfaces and texture seem to blend in with themselves, but overall the visual aspect of reality maintains.The signals that go from your brain to your body start to slow, leading you to experience "strobing" of visual and audio input. Sounds seem to be heard just slightly after they're made. Senses are dulled, though some people report an a very large olfactory increase (smell).
Closed-eyed hallucinations do not necessarily occur at this plateau, but imagination is vastly augmented to the point where one can somewhat recreate a semi-real environment in their mind (probably formed from the infinite shapes and patterns that make up the cells in your eyes). Pain becomes very slightly dulled as the signals to the brain get interrupted. Your experiences throughout the day will guide and set an outline of the imagery you might see, which is significantly different from psychedelics.
Other than realizing this, you also can barely move. The amphetamine-like boost and any of the stimulating effects subside, to be replaced by a growing dissociation, similar (to an extent) to a dose of ketamine, but much longer.
From the DXM FAQ:
The flanging of visual effects, coupled with the loss of stereoscopic vision, becomes so strong that the brain seems to completely give up trying to process vision, leading to a sort of "chaotic blindness". Simple images (e.g., a candle flame) are still recognizable, although given the loss of stereoscopic vision one tends to see two of everything. More complex images, especially images that are not sharply defined, are difficult if not impossible to recognize. Vision, when possible, has a very dream-like quality to it.
Simple sounds are still understandable, and one can usually comprehend language, although it may be necessary for the speaker to phrase it in a complex rhythm (see Section 5.7.2). Music euphoria is rare. Touch and taste are subject to considerable anesthesia, and pain especially may be completely dissociated (it's still there, it just doesn't seem to apply). Body position, kinetic, and balance senses are similarly disrupted.
Some people continue to report an enhanced sense of smell on the third plateau; in a few people almost all smells are overpowering, and subtle elements of scents may be recognizable. This can affect taste, and ordinary foods or drinks can take on peculiar tastes as previously unknown odors are noticed. Even the type of container can affect the smell, with faint scents from paper cups, plastic, and even metal noticeable.
Hallucinations may continue, although they tend to be more abstract and "pre-sensory" rather than being predominantly visual. Oftentimes there is an overall sensation of being surrounded by "grey-ness", which brightens to white light as the dosage increases. There do seem to be more frequent moments of "virtual world" experiences, where one can construct an imaginary sensorium with the eyes closed.
At the third plateau, the flanging of sensory input occurs both on a raw level (sounds, images) and on higher levels (words, phrases, faces, etc.) This is, to my knowledge, unique to DXM. Flanging may slow down and speed up, leading to periods of lucidity alternating with periods of semi-consciousness."