Many analyses of Jekyll and Hyde discuss the duality of human character and the obsession with the primitive, evil man inside us all, begging to be let out, but many critics do not discuss how incredibly disturbing the transition actually is. They mention Jekyll and Hyde as two separate characters representing two separate ideas, but in reality they are both the same person and Dr. Jekyll is really not the ideal Victorian man most readers symbolize him as.
For example, the entire last letter describes gruesome deeds done with some remorse, but not enough based on the actions. Jekyll writes the letter in his voice; Jekyll writes the letter to Utterson, yet his descriptions about his alternate personality at the beginning of the letter show a fascination and almost fetishization. The description, for example, has a strong erotic tone to it:
“The most racking pangs succeeded: a grinding in the bones, deadly nausea, and a horror of the spirit that cannot be exceeded at the hour of birth or death. Then these agonies began swiftly to subside, and I came to myself as if out of a great sickness. There was something strange in my sensations, something indescribably new and, from its very novelty, incredibly sweet.” (57)
The language sounds sado-masochistic, and the fact that he performs this over and over again to get the same result coincides with the constant search of pleasure through pain, simulating the effects of orgasm as Deleuze and Freud wrote about. Jekyll gets pleasure out of this painful experience or else he would stop performing it over and over again. He feels a sick freedom that no one else in Victorian society, due to their strict rules, are allowed to feel.
The fact of the matter is Jekyll and Hyde, though different in appearance, are still the same exact person. Hyde comes from Jekyll, but possibly even more terrifying, Jekyll comes from Hyde. In every evil, corrupt person lies some form of goodness, which may be even scarier.