Very much as a drug addict would react to the absence of his particular drug.
The narcissist constantly consumes (really, preys upon) adoration, admiration, approval, applause, attention and other forms of Narcissistic Supply. When lacking or deficient, a Narcissistic Deficiency Dysphoria sets in. The narcissist then appears to be depressed, his movements slow down, his sleep patterns are disordered (he either sleeps too much or becomes insomniac), his eating patterns change (he gorges on food or is avoids it altogether).
He is be constantly dysphoric (sad) and anhedonic (finds no pleasure in anything, including his former pursuits, hobbies, and interests). He is subjected to violent mood swings (mainly rage attacks) and all his (visible and painful) efforts at self-control fail. He may compulsively and ritually resort to an alternative addiction - alcohol, drugs, reckless driving, shopaholism.
This gradual disintegration is the narcissist's futile effort both to escape his predicament - and to sublimate his aggressive urges. His whole behaviour seems constrained, artificial, and effortful. The narcissist gradually turns more and more mechanical, detached, and "unreal". His thoughts constantly wander or become obsessive and repetitive, his speech may falter, he appears to be far away, in a world of his narcissistic fantasies, where Narcissistic Supply is aplenty.
He withdraws from his painful existence, where others fail to appreciate his greatness, special skills and talents, potential, or achievements. The narcissist thus ceases to bestow himself upon a cruel universe, punishing it for its shortcomings, its inability to realise how unique he is.
The narcissist goes into a schizoid mode: he isolates himself, a hermit in the kingdom of his hurt. He minimises his social interactions and uses "messengers" to communicate with the outside. Devoid of energy, the narcissist can no longer pretend to succumb to social conventions. His former compliance gives way to open withdrawal (a rebellion of sorts). Smiles are transformed to frowns, courtesy becomes rudeness, emphasised etiquette used as a weapon, an outlet of aggression, an act of violence.
The narcissist, blinded by pain, seeks to restore his balance, to take another sip of the narcissistic nectar. In this quest, the narcissist turns both to and upon those nearest to him. His real attitude emerges: for him, his nearest and dearest are nothing are but tools, one-dimensional instruments of gratification, Sources of Supply or pimps of such supply, catering to his narcissistic lusts.
Having failed to procure for him his "drug' (Narcissistic Supply), the narcissist regards friends, colleagues, and even family members as dysfunctional, frustrating objects. In his wrath, he tries to mend them by forcing them to perform again, to function.
This is coupled with merciless self-flagellation, a deservedly self-inflicted punishment, the narcissist feels. In extreme cases of deprivation, the narcissist entertains suicidal thoughts, this is how deeply he loathes his self and his dependence.
Throughout, the narcissist is beset by a pervading sense of malignant nostalgia, harking back to a past, which never existed except in the thwarted fantastic grandiosity of the narcissist. The longer the lack of Narcissistic Supply, the more the narcissist glorifies, re-writes, misses and mourns this past.
This nostalgia serves to enhance other negative feelings, amounting to clinical depression. The narcissist proceeds to develop paranoia. He concocts a prosecuting world, incorporating in it his his life's events and his social milieu. This gives meaning to what is erroneously perceived by the narcissist to be a sudden shift (from over-supply to no supply).
These theories of conspiracy account for the decrease in Narcissistic Supply. The narcissist then - frightened, in pain, and in despair - embarks upon an orgy of self-destruction intended to generate "alternative Supply Sources" (attention) at any cost. The narcissist is poised to commit the ultimate narcissistic act: self-destruction in the service of self-aggrandisement.
When deprived of Narcissistic Supply - both primary AND secondary - the narcissist feels annulled, hollowed out, or mentally disembowelled. This is an overpowering sense of evaporation, disintegration into molecules of terrified anguish, helplessly and inexorably.