Abraham Lincoln: Vampire Hunter Theme of Sadness

You might expect a book titled Abraham Lincoln: Vampire Hunter to be a fun romp full of vampire slayings and people breaking out into song. In fact, Abe's story begins with him getting sad about killing a turkey and it only gets sadder from there. Historians sometimes wonder if Abe and Mary Todd Lincoln were depressive, and after reading this book, we can't help but wonder that, too. They have lots of reasons to be sad, considering how their loved ones keep dropping like flies. But Abe and Mary aren't the only sad people here; even the narrator struggles with the blues. Still, sadness can be a good thing, too, at least in the sense that it fuels Abe's sense of duty and desire for revenge.

1. What characters are most sad in this book and how do they deal with their depression? Are they any good at coping?
2. When is Abe happiest? How does the book show us he's happy? 
3. Is Abe happy at the end of the book when he is a vampire? If so, why is he happy there? And if he isn't, why not? We mean, he's immortal and all. Shouldn't he be thrilled?
4. Is Abe's sadness ever useful? Does it, for example, fuel his sense of duty? Revenge?
5. Are vampires happy or sad in this book? Do vampires get happy or sad for the same reasons as human beings?