I might be able to help you with that, Marcel.  You're not the Marcel who walks around in parks wearing white paint on your face and pretending to be trapped in invisible boxes and generally annoy people who walk by, are you?  Because, if you are, then that might account for your depression.  Or maybe it's because you just found the website, http://www."NobodyLikesAMime.com."  (It's not really a link; I just made it blue so it would look like one just to annoy a few of you.  Annoyance is terribly underrated and needs to be introduced more into our society, the Internet, especially.)

I do understand that "letdown" a writer can feel after finishing a big project.  The same kind of letdown has been noted by artists and creative people from all walks of life (even those who pretend to walk against the wind on a windless day in parks, annoying people trying to walk by without being annoyed by white-painted flexible people pretending to walk).  It seems to be a rather natural feeling to go through one of these "downers" after one has been creatively focused on something for a pronounced period of time.  Why, you ask?  I really don't know.  But I'll take the best guess I have:

DcH's Screenwriter's "Letdown" Theory:

When you take on a big project and begin to write a screenplay, an amazing transformation takes place both within and without.  For our purposes, let's focus our attention on the "within."  ("Without" being normally not a pretty sight:  your skin going pale from being inside too often from writing so much; your eyes taking on a maniacal expression from getting so many wonderful ideas for your script, looking like they're always popping out wildly.  Ergo, you've noticed your friends, neighbors, mailman, and even dogs and cats keeping more than a normal distance from you.)  Within you, however, a miraculous and awesome transformation is taking place.  As soon as you committed to writing your first or next screenplay, you sent a message to your body and, deep in the recesses of your cells, tiny, microscopic screenwriters woke up and diligently went to work and kept on working day and night (even when you slept, you callous, unfeeling taskmaster, you!), coming up with those ideas and plot points and dialogue and twists (storyline twists come from the spinal column cellular screenwriters; dialogue emanates from the screenwriters in the cells of the mouth and throat; premises come from the screenwriters in your left foot, etc.).  When you've typed "FADE OUT:" and done your rewrites and polishes, and there's nothing left to do but register and send your script to your agent or your mom, those teensy weensy screenwriters know it and, whether you like it or not, they have feelings, Mr. or Mrs. Run Them Ragged Until They Drop!  Believe, you, me (or "believe me, you," depending on what side of the equator you are on), because you haven't been paying attention to these millions of little screenwriters while you took all the credit for what you thought you were creating, you forgot about the price you will have to pay -- one way or another.  They, the millions of little screenwriters in your cells, are aware of it.  And what you should be aware of is that THEY NEVER FORGET.  Oh, sure, they'll produce when there's a deadline.  But when that deadline has been reached, when the last polish has been polished... they will be heard.  And heard loud and clear.  That "depression" you're feeling, that uncomfortable "letdown" is not what you think it is.  What you're actually experiencing is the convening of the Little Screenwriters Guild (LSG), a strong union that will not be denied.  If you listen and sense very carefully, you can hear the speakers advocating for better pay and higher ancillary residuals.  They want new and improved contracts.  And they're going to stay at the bargaining table until they get them.  Or else.

This brings us to the solution part of this monograph.  What is the best way to handle this agitation and unrest that is coming from your little screenwriters, which masks itself as depression?  Well, you could take this experimental drug that  supposedly consists of teensy weensy anti-union personnel carrying even tinier Billy clubs that violently break up cellular union gatherings.  But I wouldn't advise that method because I heard it can give you stomach aches and make you have this unexplainable urge to take a Tae Bo class and punch and kick yourself until you have to be forcibly removed.  So, what's another option to solve this dilemma?  I have found that an excellent way to combat the "Fade Out Blues" is to have another project already in the works so that you can put some of that restless, "I don't know what to do with myself now" energy somewhere.  It doesn't have to be another screenwriting project; it could be a gardening one, for that matter (or a screenplay about gardening.  Or, you could bury all your screenplays in your garden.)   Just as long as it draws your attention and you desire to accomplish it.  But before you move to your next project, I recommend that you first reward yourself for all that you've done.  Maybe take some time off.  How about a vacation?  You've earned it.

Just don't forget to make reservations for all your little friends.

They'll be watching.

I don't say any of this to make you paranoid.  But  if you want them to come up with another good script while you live like a king or queen off their blood, sweat and tears, if I were you, I'd get each of them a separate room. 

Just a suggestion.

I have to go now.  They just told me they want a sauna.  And I don't want to disappoint them... Again.

DcH