One day we someone is going to do a full clinical retroactive study of Sanji's descent into madness once the series concludes. Perhaps it started when Bon Kurei started to mess with his mind? Being driven to impotence through his own chivalry when facing Kalifa? Seeing his deepest desire and subconscious motivation shatter upon seeing Kokoro as his first mermaid contact? Essentially looking at a criminally insane reflection of himself when meeting Absalom? Then driven mad through his own his own fears (and possible hidden desires) of emasculation for 2 years on Kammabakka?
The timeskip reunion is essentially a fractured personality desperately trying to reestablish himself as a Straw Hat and in society as a whole. The sudden shocks of seeing Hancock and a veritable harem of mermaids shocked his already strained mind to suffer actual physical impairment. Now Chopper notices what a wreck of a man Sanji has become and begins his case study, attempting to shield his fragile mind of his dangerously sensuous surroundings.
His efforts appear to rehabilitate him until a fateful day on Punk Hazard where another deeper fantasy is realized–being mentally transplanted into Nami's body. Naturally his unstable mind struggles between maintaining some form of self-control and indulging in impulses driven by pure id. While it seems all is lost at this point, this very curse also acted as a remedy in that something that was once a source of obsession eventually became mundane to the point where he was able to essentially transform himself back to his old confident self in this beauteous form. While his transformation back is a bit of a shock, he is not overly sullen over it.
Yet his romantic fantasies are not abated, because he soon crosses paths with Tashigi and her men. Suddenly stuck with a damsel in distress scenario he rushes to their aid in reckless abandon and nearly crippling himself in the face of a far more rational and cool-headed foe. Miraculously he manages to distract him and fulfill his wish in rescuing Tashigi and her men. So taken in by this fantasy he doesn't realize that she is a Naval Officer who normally has orders to take him and his friends in custody dead or alive. Yet caught unawares by this brazenly chivalrous act, both her and her men too forget the Naval Code and join forces with the love-crazed rogue, turning his fantasy into reality. This confusion lasts up to the point where they part ways, reasserting Sanji's self image.
The most recent stage seems to be the more defining beginning with his infatuation and romantic experience with Violet. While casually entranced by her rhythmic dancing, he suddenly finds himself thrust into the role of a knight in shining armor protecting a fair maiden who went so far as to come to him out of the blue. In almost complete awe and joy at his good fortune, he completely forgets his mission and becomes putty in her hands. Yet instead of a knight he's more like a slave, doing virtually anything for even the slightest romantic gesture in return, even going so far as to murder a complete stranger on command. His will is no longer his own and the romance is completely one-sided.
With his rational mind completely smothered by such an overwhelming fantasy, yet again a handicap becomes an asset when Violet unmasks herself and begins to torture the deluded Sanji for information. Given how detached from reality he has become, he can speak of nothing but his romantic dreams and thoughts of her. At one point he becomes rational enough to at least discern that she is in deeper trouble than she has let on. Fed up with this seeming jest, she peers in his mind to seek the truth. Yet what she finds is a ravaged mind completely consumed with with romantic fantasy. Stunned she looks away, instinctively fearing that gazing any longer may reduce her to a vegetative state. However, she found a sort of purity in the madness she never knew existed in the mind of man and becomes another who has succumbed to his romantic fantasy.
This leads to her divulging information about her plight and causing Sanji to suddenly remember what his captain ordered him to do. While still not completely free of Violet's charm, he nonetheless aids his crew with vital info and physically comes to the rescue after Violet implants him with the image of an endangered Nami. Acting completely on instinct, Sanji reaches Doflanimgo just in the nick of time and at a speed scarcely assumed humanely possible. Yet the combination of the strain of reaching Doflamingo in time and his clouded mind made him little more than a nuisance to Doflamingo than anything.
The sudden shock of nearly being executed by Doflamingo and being among his crewmates again appears to have snapped Sanji back to normal for the first part. This in addition to being thrust into a position of crew responsibility he has never held before. So far he seems to behaving like his old rational, self-confident self. Even Chopper has deemed him mentally fit for command.
Only time will tell how long this will last and if he's on the road to recovery as the rest of Sanji's adventures come to light.
