keeping your tone when writing a novel

This is only my second post this month. Going through my marriage separation and my mother's unexpected illness has left me drained and numb. Today I found comfort in these words by Norman Mailer on stamina and writing a novel:

"A large part of writing a novel is to keep your tone. I love starting a book; I usually like finishing one. It's the long middle stretches that call on your character -- all that in-between! -- those months or years when you have to report to work almost every day. You don't write novels by putting in two brilliant hours a week. You don't write novels if you lose too many mornings and afternoons to a hangover."

I'm in that long middle in-between and have, quite honestly, let my life circumstances shut me down. But, now it's time to wake-up, shake it off, and get back to work. As Mailer puts it, "There's nothing glorious about being a professional.. . . Professionalism probably comes down to being able to work on a bad day."

I've had too many bad days lately.