Writing a book: The ultimate thrill, and a weary author

As I take a break from creating my next adventure, I am always amazed at how exhausted I feel, as if I've just run a marathon. Three solid hours of writing, and all the emotions that I've just subjected my characters to, are still draining out of me. I'm living multiple lives from the comfort of my chair.
This is also the time when I go through about half an hour of anxiety, excitement and doubts. I love what I've written, but will my readers? What if they hate it? Maybe I should change that scene completely. How the hell did I ever imagine I could write?
I don't read a book anymore, without wondering what the author went through to put their work together. Maybe this is something I've carried over from my acting days, but I can't help it. I'm invested in my characters, and want them to be as real to the reader as they are to me.
By the time I am ready to publish, I'm like the mad scientist of Frankenstein, hair a bit crazy, wild look in the eyes, laughing hysterically, "It's alive!!"
What a feeling!! Who wouldn't be an author?