Darwin was thinking during his walks. During his writing tasks much of the activity was mechanical or the consolidation of notions arrived at during leisure. What society regards as 'work' largely comprises the application of existing knowledge and the running of errands.
>He was passionate and driven, so much so that he was given to anxiety attacks over his ideas and their implications.
Emotions driving emotions? No, he was right to be anxious about the consequences of his work. Though marvellous and important and interesting, not to mention true, it set up a huge conflict in the psyche of the West due to the competing claims of science and religion. Which still hasn't been resolved.