It's overwhelming, isn't it? And so exciting! After all the work and hope and despair and sweat and tears and despair and booze and chocolate and despair SOMEBODY LIKES YOU THEY REALLY REALLY LIKE YOU!
Because what if other people like you, too?
I see this very thing happen occasionally as an editor, too. Every once in a while I get in touch with an unagented author and say, I want your book! I will give you this money!
And the author replies in like TWO SECONDS with something along the lines of "YES! YESYESYES YESYESYES YESSEYYS YEYEYS YSYEYY ERYEY EYIEL DMMG TNZBNIE!"
And I think, "Oh, yikes. No questions about escalations? No polite query about a slightly higher advance? No discussion of where I see the book development going? I would hate to think what would have happened if I were the type of editor to abuse such trust. You, sweetheart, need an agent and some Ritalin, stat."
Enthusiasm is a wonderful, wonderful thing and possibly the only thing this stupid industry runs on. But still, do everything you can to BE CALM and think things through. Please. Because I like you.