Writers react to finishing a piece of work in a variety of ways. Harold Pinter, for example, was known for carefully laying down a just-completed manuscript, staring wistfully out of the window for a moment, then shouting out of the open door to Lady Antonia Fraser, 'COME QUICK, I DONE A BIG WORDY!'
Having just completed the fourth, and possibly final draft of episode two of 18th Century comedy/drama biopic thing (we're working on a catchier title), I like to say farewell via my own personal method of a prolonged rehearsal of the awards speech, including what I'll be wearing (my never-actually-worn black linen suit, which will mean losing a stone at the very least) and those members of my posse to whom I will grant a 'shout out' (currently Dappy from N-Dubz is out, Jenny Uglow very much in).
Anyway, in case it sounds like I've gone all Gervais, there's actually quite a practical reason for this. So few projects ever actually make it to the screen (and Ep 2 of 18thC Thing is the last one before the BBC decide whether to commission a series or not), you may as well go completely mental when you do actually finish something. If you don't go completely over the top re. mentally casting the final talent available (and if I'm too busy, various members of the Green Wing cast would probably do), who's going to be on the soundtrack etc, when it almost inevitably fails to be commissioned, there's often a small sad moment when you realise you didn't even get to have a nice daydream about the whole thing, in which case you may as well have a proper job, involving heavy lifting, or working after three in the afternoon or something. DEATH, essentially.
*goes back to fondly thinking about string quartet covers of Radiohead*