It is important to make a distinction between pain and bad feelings. In the brain neuroscientists identified two neurological circuits involved with pain. One processes pain data from the body and one is a backup system that can duplicate the data from the body in case the body stops sending this data. If people complain about pains it is a good idea to have them checked out by a doctor first before applying NLP.

Pain teaches us that the location of where the pain  is felt is a projection of the brain. There is the so called rubber hand illusion that shows that the brain is easily tricked into feeling pain (or any other feeling) in a rubber hand rather than in the body.

Pain is something different from pleasure – I mean to say, it is not its opposite. If the essence of pleasure has been accurately described as a feeling of more power (thus as a feeling of differentiation that presupposes comparison), this doesn’t mean the essence of unpleasure has thus been defined. The false oppositions believed in by the common people and consequently by language have always been dangerous shackles for the course of truth. There are even cases where a kind of pleasure is conditioned by a certain rhythmic succession of small unpleasurable stimuli: this leads to a very rapid growth of the feeling of power, the feeling of pleasure. This is the case, e.g., in tickling, including the sexual tickling in the act of coitus: here we see unpleasure working as an ingredient in pleasure. It seems a little resistance is overcome and is immediately followed by another little resistance, which in turn is overcome – this play of resistance and victory most strongly stimulates that overall feeling of surplus, excessive power, that feeling which amounts to the essence of pleasure. – The reverse, an augmentation of the feeling of pain through little interpolated pleasurable stimuli, doesn’t exist: pleasure and pain are, precisely, not the reverse of one another. – Pain is an intellectual process in which a judgement makes itself unmistakeably heard – the judgement ‘harmful’, into which long experience has accumulated. In itself there is no pain. It is not the wound that hurts; it is the experience of what grave consequences a wound can have for the organism as a whole that speaks in the shape of that deep agitation called unpleasure (in the case of harmful influences unknown to earlier men, e.g., from new combinations of toxic chemicals, pain bears no witness – and we are undone …). In pain, the really specific thing is always the long agitation, the after-trembling of a terrifying shock in the cerebral focus of the nervous system: one’s suffering is not actually due to the cause of the pain (some injury, for example) but to the long-lasting upset of equilibrium proceeding from that shock. Pain is a sickness ofthe cerebral nerve centres – whereas pleasure is by no means a sickness …- That pain is the cause of counter-movements may be supported by appearances and even by the prejudice of philosophers; but in sudden cases, if one looks closely, the counter-movement manifestly arrives earlier than the feeling of pain. I’d be in a sorry plight if, having stumbled, I had to wait until the fact struck the bell of consciousness and a hint of what to do was telegraphed back … Instead, I distinguish as clearly as possible that the counter-movement of the foot happens first, to prevent a fall, and then, after a measurable passage of time, a kind of painful wave suddenly makes itself felt in the front of my head. One does not, thus, react to the pain. Pain is afterwards projected into the injured place – but the essence of this local pain is, nevertheless, not the expression of the type of local injury: it’s merely a place-sign, appropriate to the injury in strength and tone, that the nerve centres have received from it. If the organism’s muscular strength drops measurably as a consequence of the shock, this by no means indicates that the essence of pain should be sought in a lessening of the feeling of power … To repeat, one does not react to pain: unpleasure is not a ’cause’ of actions, pain itself is a reaction, the counter-movement is another and earlier reaction – the two things originate in different places.

Notebook 14, spring 1888 paragraph 173