I found this nifty essay by A.S. Byatt on the origins of Possession. I particularly liked the first paragraph about scholars becoming possessed by dead minds. I know this feeling well. Here is that paragraph:
The beginning of Possession, and the first choice, was most unusually for me, the title. I thought of it in the British Library, watching that great Coleridge scholar, Kathleen Coburn, circumambulating the catalogue. I thought: she has given all her life to his thoughts, and then I thought: she has mediated his thoughts to me. And then I thought "Does he possess her, or does she possess him? There could be a novel called Possession about the relations between living and dead minds." This must have been in the late sixties. It was the time of the nouveau roman, of the novel as "text."