Easily the most iconic theme of the Jekyll and Hyde story is when Dr. Jekyll transforms into Mr. Hyde. In the original story, Hyde was described as being shorter, uglier, and younger-looking than Jekyll. This means that when Jekyll drinks his potion, he physically transforms into a different person, not just mentally. Anyone who has endured cosmetic and reconstructive surgery knows how painful it is to restructure your body into another form. That is from months of surgery and subsequent physical therapy. Imagine enduring that much combined pain in a matter of minutes instead of months.
Due to the agony one must endure from physically changing their body, I will be drawing inspiration from the transformation scene from An American Werewolf in London.