In the now published entries it can be read that only a few weeks after an operation he had to endure because of a cancer diagnosis, he decided to continue impersonating Snape despite his illness. So it says in 2005, just before the start of ‘Harry Potter and the Order of the Phoenix’: “Finally: Yes to HP 5. The feeling is undecided. The argument that wins is what says: ‘Go through with it. It is your story.’
Five years earlier, he wrote that he “felt a little nothing” while preparing for his role when reading the first HP volume. It’s exciting to see how that feeling changes as work begins and he learns of Snape’s love for Lilly.