congratulations and condolences...the same emotions happen to actors at an end of a run...you become so connected to the character, if done well, then bang all gone/all done...and on to the next.

As a writer, I have six drafts in the pipeline to avoid that 'over' feeling. Hope your book sells!

BTW--my acting career started next door to the Iowa Writer's Program! In a writing course I described a women waiting at the bus stop who was my 'human alarm clock' --the instructor reading the piece called out "Who lives at 52 Hawkeye drive?" He lived 3 doors down, used the same lady's arival at the stop as his human timer. He was in the writer's program.