It's not uncommon for people who've planned and plotted and daydreamed and replanned to find out they can't bring themselves to write. Sometimes it's fear of messing up what is such an excellent story in their heads, of not being able to live up to their own story. Sometimes it's simple exhaustion from having done so much planning; they're sick of the story now. Sometimes (like me, one of the people neuro was talking about) once they've done all that work they feel they've told the story and any impetus to re-tell it in narrative form is gone.
That said, there's no cure. None. All you can do is write. Write anyway, write even if you don't feel like it, write the worst schlock imaginable. Because it's ok if it's terrible.
It really is ok if it's terrible.
It's ok because you can edit it. What you CAN'T do is edit a blank page, as the saying goes. You need to get all the words down before you can go back and fix the bad ones. You can't fix plot holes or weak characterization until you've written plot holes and weak characters.
So yeah, like Enj said, butt to chair. Start writing. Don't get up until you've met a wordcount goal. It doesn't have to be grand. I know people who say 500 words a day, or even only 300. You can up it later if you find yourself loosening up, but it's something external to the story to give you hope that you will soon "be done", and yet you'll feel like you got something accomplished. It's also a big help if you do it at the same time every day.
Honestly, the feeling will get better. In the end, what you've been doing is great, but it's not writing and only writing makes writing easier. You'll see. In a week or so, you'll have blown the rust off your talent and the words will come easier.
