They tell you there will be a day after, you grow up and realize on your own that there will be a day after, but when it comes, you are unprepared for it. The day after Christmas, the day after your book is published, the day after you graduate, the day after you're married.
It's not the day you planned.
Nor is it the poem you planned. This is the first step in any creative endeavor - to acknowledge that reality stinks and you better write/live/fantasize your way into something better. Ribbons strewn beneath the table, wedding cake stashed in the freezer, review copies in the mail, gifts stacked neatly on top of the list of thankyou cards to write and/or people to put on your gift list next year - it's all now detritus of the midnight Santa vigil, that sweet rush of anticipation that heralds any birth. Now, you sit amid the after-birth wondering why you got so excited. And how long it will take you to take down the Christmas tree.
A good time to create unfinished drafts, blog, read blogs. I just discovered one by an anonymous member of the publishing profession, which will presumably dish enough dirt to justify the anon status of its author. It's only a month old, but already looks quite promising for those bitchy moments after you get your annual rejection letter from Poetry magazine, etc.
My advice: belch, then write. Don't send anything out. Don't open the mail. Let the tree molder until that poem's done.