Empty Novel Syndrome?

So my novel is being sent around to different publishers by my agent, Rubin Pfeffer of East/West Literary Agency. It's a very thrilling thing.

But I'm wondering.

I said "go out and make your way in the world," and my novel is grown and gone. This six-year world is suddenly empty and I find myself curiously lonely and puzzled.

What do I write now?

Surely those of you who have experienced this know just what to do. You had another manuscript on the back burner. You had several. You're working on your tri-quels. But this is all very new to me. Never wrote a long story before. Never thought anyone would want to see it.

I kind of miss my characters, my places, my plot.

Maybe this is what Empty Nest Syndrome feels like.