[quote author=lostinself]
Still i find it hard to accept regarding some of the jamais-vu type stuff i've experienced. Derealization is a horrible state to find oneself in; luckily it's temporary in most cases.
[/quote]
There are pathological states of this "derealization"" found in people suffering from trauma, Parkinson's disease as well as schizo-spectrum disorders where there is a failure of the neural circuitry to adequately integrate the various perceptual inputs which forms the physiological foundation of our "selfhood".
On the other hand, there is a sort of new realization which can happen when one who is habitually dissociated can literally re-member and re-engage with one's own self and one's surroundings. I would guess that in this case, the perceptual shift occurs due to a relatively more efficient collection and integration of perceptual inputs than when one was habitually dissociated.
So in both cases there is a perceptual shift - but in different directions leading to different experiences.
Let me try an analogy here. It is known from neurology that different perceptual inputs (visual, auditory, olfactory, tactile etc) are processed at different speeds. Still, for inputs arriving within a certain time window, the brain integrates everything and provides a context to us such that it appears simultaneous to us. The analogy would be a movie camera which is taking pictures at a certain shutter speed and frame rate to capture the reality. Shutter speed determines what how long one frame is exposed; the frames are then integrated, processed and played back to show the movie. Depending on the relative shutter speeds and frame rates one we can see more or less details, have crisp or blurry images and smooth or choppy playback. We can have a completely different picture of reality when we change these parameters.
The pleasurable jamais vu experiences can be caused by what is called an "expanded present". A slightly diffused and open focus allows more information to simultaneously enter the present moment and if the inputs can be processed adequately, we get to a richer context. This is experienced in certain meditative techniques and is accompanied by specific brain waves (
this thread has some details).