Here's a breakdown of how this unfolds:
* Jekyll's initial optimism: Initially, Jekyll is confident in his ability to control his transformation into Hyde, believing he can revert back at will. He even boasts to Lanyon that he's "got the mastery over it" and "can cast it off at will."
* The first sign of trouble: However, the first real warning sign comes when Jekyll experiences a change into Hyde without taking the potion. This shows that the transformation has begun to exert a control over him.
* Loss of control: As the chapter progresses, Jekyll experiences increasing difficulty controlling his transformation. He realizes he is becoming more and more Hyde-like, even in his normal state. This fear is amplified when he finds himself trapped in his Hyde form for an extended period, unable to change back.
* The terrifying truth: The final blow comes when Jekyll realizes that his transformation isn't just a temporary change but a permanent, irreversible process. He understands that his duality is no longer a choice, but a reality he cannot escape. This realization is utterly terrifying for Jekyll, marking a turning point in his story and fueling his descent into despair and ultimate demise.
In short, Chapter 5 unveils the truth about Jekyll's transformation - it's not a manageable duality, but a horrifyingly irreversible and inescapable metamorphosis. This realization is the catalyst for the rest of the story, driving Jekyll's desperation and eventual downfall.